(CNN) -- The parents of a Virginia Tech student who disappeared last month during a Metallica concert asked Wednesday for volunteers to help conduct a community search this weekend.
Morgan Harrington, a 20-year-old education major, went to the concert at the University of Virginia's John Paul Jones Arena in Charlottesville, Virginia, on October 17. Police said they are continuing to follow leads in the case, but have no new information.
"We will stop at nothing until she is found," Harrington's father, Dan Harrington of Roanoke, Virginia, told reporters Wednesday.
During the concert, Harrington left her friends to use the restroom, Virginia State Police spokeswoman Corinne Geller said Wednesday, and when she did not return they called her on her cell phone at 8:48 p.m. She told them she was outside the arena and could not get back in because of its policy, Geller said, but told them not to worry about her and that she would find a ride home.
There are restrooms inside the arena, Geller said, and police do not know how or why Harrington got outside. Witnesses who saw her outside the arena said she did not appear to be with anyone, Geller said.
At about 9:30 p.m. that night, witnesses reported seeing a person matching Harrington's description walking on a nearby bridge, Geller said. No further sightings were reported.
Harrington's purse, with her identification and cell phone inside, was found the following day in an overflow parking lot near the arena, Geller said. A friend had driven Harrington's car to the concert, she said, and so was still in possession of the car keys when they got separated. Police would not say whether Harrington was intoxicated.
A $150,000 reward has been offered for information leading to Harrington's whereabouts, Geller said. Of that, Metallica contributed $50,000.
Authorities have received more than 350 leads since Harrington disappeared, Geller said. She was reported missing the day after the concert, when she did not show up at her parents' home to study for a math exam with her father.
Working with police and the Texas-based Laura Recovery Center, the Harringtons organized the community search to begin Friday and reconvene Saturday or Sunday.
The couple was joined at the Wednesday press conference by Ed Smart, whose daughter Elizabeth was abducted in 2002. She returned home nine months later after police found her in the custody of suspect Brian David Mitchell and his wife, Wanda Barzee.
"When a child is missing, you have no idea of what to do and how to move forward," Smart said, calling it "the club that nobody wants to belong to."
"There isn't a parent out there that would want to be in his position," he said of Harrington. "The importance of it is, there's a girl that is lost out there that needs to be found."
Harrington said he reached out to Smart last week to seek advice on how to go through the disappearance of a child. Smart has been supportive and helpful, he said, and offered to come to Virginia and speak to reporters Wednesday.
Gil Harrington spoke briefly. "Morgan, two-for-one," she said, referring to a motto on a Web site set up by the family, www.findmorgan.com: "I love you too much, forever and once more."
"We are trying to find you," she told her daughter. "We will never stop. We are trying, honey, hang on. And to the person who has taken Morgan from us, please just let her go."
Dan Harrington said Smart's story had provided them with hope.
"People do come back," he said. "Not everyone is lost. We have to hold out hope that our daughter will return to us."
Smart told reporters he never lost hope that his daughter was alive, but "that doesn't mean there wasn't doubt at times."
"I believed she was still out there and felt that she would come home," he said. "That's what we're hoping for with Morgan. We just want to see her come home ... I believe that somebody can help us."
Harrington is 5 feet 6 inches tall and weighs 120 pounds, with blond hair and blue eyes. She was wearing a black Pantera T-shirt, a black miniskirt, black tights and black boots when last seen.