(CNN) -- Sure, everyone knows that Oprah, Shaq and Ashton Kutcher are huge on Twitter. They're famous -- they should be huge on Twitter.
But Heather Armstrong? John Dickerson? Adventure Girl? These people can stroll unmolested through a paparazzi convention, and yet each has more than 1.2 million Twitter followers -- enough to rank them in the top 200 overall and more than Stephen Colbert, Snoop Dogg or Paris Hilton.
To thrive on the popular micro-blogging site, celebrity isn't always enough. You also must have something to say.
"You can't be Moses shouting down the mountain on Twitter," says Brandon Mendelson, a blogger who has amassed almost a million Twitter followers. "You need to be that friend everyone wants to hang out with."
Here's a look at five Twitterers you may not have heard of. They don't show up in the tabloids or on Leno. But they have the power, through the viral effect of their retweets, to make things happen, and maybe even nudge the national conversation a little.
Heather Armstrong: @dooce
If her real name doesn't ring a bell, the name of her blog might. Armstrong launched Dooce.com in 2001 and soon built an audience for her deeply personal, brutally honest posts about married life, kids and a postpartum depression that landed her in a mental hospital.
Some Bay Area friends turned Armstrong onto Twitter in early 2007, but her popularity on the site didn't really take off until this year.
"Since February it's sort of exploded," says Armstrong, who lives in Salt Lake City, Utah, with her husband and two daughters. "I find myself enjoying it more as my audience has grown. I also feel more pressure to do it -- to keep things updated and to keep things interesting."
Armstrong's tweets find sardonic humor in mundane domestic life, such as a recent one about offering to be her resistant daughter's "personal booger servant" by cleaning out her nose.
"It's a different muscle in the brain than the one you use to blog," she says of Twitter's 140-character limit. "And I had to learn how to exercise that muscle." Asked what makes a good tweet, she said, "Something profound. Something very funny. It's an art form, I think, to do it really well."
Armstrong checks Twitter first thing every morning on her iPhone, and often learns of breaking news there before she hears it anywhere else.
Two recent incidents awakened her to Twitter's growing influence. Armstrong spent $1,300 on a washing machine that broke almost immediately. After the manufacturer balked at fixing the problem, Armstrong began ranting on Twitter. The company sent someone to repair the washer within 24 hours.
Armstrong also reached out to her nearly 1.4 million Twitter followers for help in locating her assistant's mentally disabled brother after he went missing last month in Phoenix, Arizona. He was found several days later and identified by people who'd seen the news on Twitter.
"I sort of feel like that's one of my callings now, finding missing persons through Twitter," Armstrong says. "The power of it is really mind-boggling."
Stefanie "Adventure Girl" Michaels: @adventuregirl
This former bikini model branded herself as Adventure Girl and launched a second career as an online travel journalist in the mid-1990s, well before the Internet was in every household. Despite being late to Twitter -- she joined in March -- Michaels has amassed more than 1.2 million followers.
"I pinch myself every morning," says the Los Angeles, California, resident, who was an unemployed magazine writer last fall until she discovered micro-blogging. "I can't believe that even one person wants to hear what I have to say. I really owe everything to Twitter. It changed my life."
Michaels believes she found a niche on Twitter because few people were writing about travel. Her enthusiastic tweets mix travel tips and suggestions with details about her personal life and plugs for charitable causes such as Operation Smile, which provides corrective surgery for children with cleft palates.
Twitter's quick bursts of thought fit Michaels' on-the-go lifestyle perfectly.
"If you can't say it in 140 [characters], you shouldn't be saying it. It's made me a better writer ... because you find a way to get to the point," she says. "People don't have time to read those lengthy, self-serving blogs anymore."
So how did she get so many followers?
"I'm on all the time. When you start doing this all the time, and you engage [with people], and people know you care ... that's when you grow," she says. "It goes viral very quickly. And once you go viral, you're golden."
Michaels posts up to 50 tweets a day, often from her ever-present BlackBerry while she's on the road.
"It's fascinating to take your tweets along with you [when you travel]," she says. "It's like you're never alone."
Brandon Mendelson: @BJMendelson
Mendelson, a writer from Glens Falls, New York, applied unsuccessfully for a job at Twitter and even quit tweeting for a while last year. So what's he doing with almost 1 million followers?
He and his wife spent several months earlier this year criss-crossing the country to promote early detection of breast cancer, which has afflicted many women in his family. Their charitable efforts landed Mendelson on Twitter's Suggested User List, which suddenly brought him as many as 5,000 new followers per day.
"It's funny," says Mendelson, who writes a blog called Soap Box Included. "You spend 10 years doing something, not getting anywhere with it, and all it takes is one flick of a switch, and there you are."
Mendelson calls himself "the most followed non-brand, non-celebrity, non-media outlet on Twitter." It can be a mixed blessing. Like all popular Twitterers, he has been besieged on the site by opportunists.
"All they wanted to know were Twitter tips and how to make money. They didn't care about anything else," he says. "I'm doing my best to push out those folks."
Mendelson's work has been published on Mashable, the Huffington Post and other places. He believes Twitter forces people to choose their words wisely, an important lesson for everyone.
"My God, most tweets are extremely boring," he says. "It's not the stereotypical 'I just ate a sandwich' junk either. It's the people who read those terrible Twitter and social media books and decide to act like robots to gain followers."
To Mendelson, the number of followers someone has on Twitter isn't necessarily as important as the passion of the followers.
"You don't need a million to be successful, not if you have 10,000 people who are engaged with you, retweeting you and ready to buy your book or see your movie," he says. "At that point, if your stuff is good, it'll spread on its own."
Veronica Belmont: @Veronica
If you were to draft a blueprint for becoming a Web starlet, you could do worse than follow Belmont's example.
A background in new media? Check. Host of geek-culture webcasts about gaming and technology? Check. Bay Area home, close to visibility-boosting tech conferences? Yup. Young, bubbly camera presence? Yep, that too.
Belmont, 27, parlayed a CNET internship into several video hosting gigs, including her current job with the "Tekzilla" show on Web TV network Revision3. The San Francisco, California, blogger was among Twitter's earliest adopters in 2006 and has used it consistently since.
"It definitely keeps things pithy!" she says of Twitter's space limit. "I find that little anecdotes pop into my head and it drives me nuts if for some reason I can't commit them to Twitter at that very moment.
"The main change I've seen in my blog writing is that I don't do it as often -- ideas that I usually would have expanded out to a couple of paragraphs for a blog post end up getting the 140-character treatment instead."
Like Mendelson, Belmont saw her army of followers -- now almost 1.4 million -- explode after she made Twitter's Suggested User List.
"For a good amount of time I was the most-followed female on Twitter," she says. It's a blessing and a curse, sometimes, since you get a lot more people introduced to your work, but they might not always be your target audience. They aren't always as interested in the tech side of things."
Belmont's favorite tweets contain a link and a little bit of analysis. She tries to "keep things light and funny" and use non-sequiturs, which seem to get people's attention.
"I learn something or meet someone new almost every day on Twitter," she says. "It's definitely helped me make a lot of industry connections, but I value it most for the instant feedback on stuff I'm working on. I'm not sure how much different my life would be right now without it, but it would be very hard to give it up."
John Dickerson: @jdickerson
This veteran political reporter first created some Twitter buzz by tweeting about Fox TV host Bill O'Reilly shoving a Barack Obama aide during a 2008 presidential campaign event in New Hampshire.
"My favorite campaign tweets, though, were far more mundane," said Dickerson, Slate's chief political correspondent. "They were all the ones that just conveyed the day to day of what it was like."
The former Time magazine reporter joined Twitter in 2007, although in a way, he was tweeting long before that.
"For years I've carried a notebook. In it I've written observations, odd thoughts, quotes and any notion that's come into my head. I was using Twitter for years before Twitter existed. As a reporter, part of my job is to take people places they can't go. Twitter is a super fast way to do that."
Dickerson actually has two Twitter accounts. The one that plugs his Slate pieces and CBS-TV appearances has about 2,300 followers. The other, where you can find such witty musings as, "Does this new BlackBerry make my Tweets look fat?" has 1.2 million.
He's still not sure how he got so popular. "I think there's been a computer glitch that they haven't discovered yet."
Dickerson is wary of people who use their Twitter accounts to promote themselves, which might explain why he doesn't think much of most members of Congress' attempts at tweeting.
"I like [Iowa Republican] Chuck Grassley because he's blunt," he says. "Most are truly dreadful."
Dickerson believes a good tweet conveys useful information or a personal observation in a funny or sideways way. And it can't be boring.
"Shorter is always better," he says of Twitter's 140-character limit. "If there were any more space Twitter would stop being a lovely little toffee candy and turn into something more confused."