(CNN) -- A new study finds that 54 percent of teens talk about behaviors such as sex, alcohol use, and violence on the social networking giant MySpace -- presenting potential risks even if all they're doing is talking, researchers said Monday.
Do you know what your teen has posted on social networking Web sites?
The study looked at MySpace profiles of 500 people who identified themselves as 18-year-old males and females in the United States. References to risky behaviors included both words and photos, the authors said.
Not all teens who write about risky behaviors in their profiles actually engage in them in real life, said Dr. Megan Moreno of the University of Wisconsin School of Medicine and Public Health, one of the authors of the study, which appears in the January issue of Archives of Pediatrics & Adolescent Medicine.
They may instead talk about sex, substance use, or violence because they are contemplating doing those things, or because they want to brag without actually doing what they say, Moreno said.
Even if teens have not actually engaged in risky behaviors but merely brag about them online, this can still affect their future behavior, said study co-author Dr. Dimitri Christakis, professor of pediatrics at the University of Washington and director of the Center for Child Health, Behavior and Development at Seattle Children's Hospital.
Those who lie about the behaviors to show off may receive positive feedback from others -- comments such as "that's great" or "I do the same thing" -- that encourage them to actually try out the behaviors, he said.
Apart from that, teens who claim such behaviors are more likely to be victims of bullying and unwanted invitations for sex, he said.
In a second study, Moreno and colleagues identified 190 profiles of 18- to 20-year-olds that contained three or more references to sexual behaviors or substance abuse. The authors then made a profile of their own, called "Dr. Meg," from which they sent a single e-mail to half these profiles, warning them about the risky information and offering information about clinical resources.
They found that, after three months, 42.1 percent of the profile owners who received the e-mail -- and 29.5 percent of those who did not -- either removed references to risky behaviors or made their profiles private.
"It's really not that MySpace is bad or good. I think the lesson is that it's a tool, and how you use it determines the kinds of outcome you're going to get," Moreno said.
Experts say the bottom line is that parents should get more involved in the online lives of their children.
"I tell parents that they should absolutely create their own MySpace and Facebook page," Christakis said. The study inspired him to create his own Facebook account, and his 10-year-old already wants to know about his "friends," he said.
In some cases, parents should even have their children's passwords for these social networking sites, especially when the children are around age 13 or 14, said Vivian Friedman, child-adolescent psychologist at the University of Alabama at Birmingham.
Friedman was not involved with the study, but she is well aware of the problem. One of Friedman's patients, the daughter of a preacher, posted nude photographs of herself online, a move that cost her father his job, Friedman said.
But she said 54 percent as a figure for profiles with risky behaviors seems too high, given that most of what happens on social networking sites is "chit-chat."
"I have parents that catch their kids bragging about something on MySpace, and when you actually confront them, the kid says 'I really wasn't doing it,' and they can prove they were not at the party where they were supposed to have been drinking," she said.
Beyond keeping a watchful eye on risky interests and pictures, parents should also use social networking sites such as MySpace -- which had about 120 million users as of this summer -- as an opportunity to learn about their childrens' favorite movies and hobbies, as well as their top friends, she said.
"You so often hear parents say 'I don't even know my kid anymore.' Here's a very easy tool to get to know your kid again," she said. ,