"I beg of everyone that hears this broadcast, if they know anything at all about where my daughter, Michelle, is today, or where she might have been Friday night, Saturday morning, they tell us instantly," John-Charles Quinn said in the video posted on the Burlington Police Department Web site.
Meanwhile, fliers went up, police fanned out and students at school hoped against hope as the search continued into a second day.
Michelle Gardner-Quinn, a 21-year-old senior from Arlington, Va., was reported missing Saturday after failing to show up for dinner with her parents. She was last seen heading home from a night on the town, and college officials and fellow students alike worried she may have been a victim of foul play.
"She's out of place with no logical explanation for being out of place," Det. Kim Edwards said. "At this point we do not believe she left on her own free will."
Police called the disappearance "highly suspicious" and said there was concern Gardner-Quinn may have fallen prey to a man who tried to lure a woman into his car at about the same time she was last seen, about three-quarters of a mile away.
That woman told police the man — in his 20s, driving a white "Subaru-type" hatchback vehicle and wearing a baseball cap and gray hooded sweat shirt — asked her to get into the car and she refused, according to Police Chief Thomas Tremblay.
According to Tremblay, the incident happened about 20 minutes after Gardner-Quinn was last seen, but he said it was unclear if that was related and he conceded that investigators were struggling for leads.
"We consider Michelle's disappearance to be highly suspicious and time is essential as this investigation enters its third day," the chief said at an afternoon news conference.
"We're going to remain hopeful until there's a reason not to," said Deputy Police Chief Michael Schirling.
Gardner-Quinn, a senior majoring in Latin American studies and environmental science, went out Friday with a group of friends to celebrate one's 21st birthday at several downtown bars. She parted with the group about 2:15 a.m. to walk back up the hill toward campus, accompanied by a person her friends described as "a random guy."
She hasn't been seen since.
The timing of the disappearance — during parents' weekend, with her parents at the university to visit her — fueled fears that something bad happened to her.
"Just based on what we know about her from her friends and family, it's not like her not to at least call, and especially if your parents are here from a whole other state hours and hours away, here just for the weekend," Det. Ray Nails told CBS affiliate WCAX. "To do something like that is completely out of her character."
Her parents reported her missing Saturday night after Gardner-Quinn failed to show up for a planned visit with them, Edwards said.
"We have many detectives working on the case round the clock," Edwards said. "We've been here all night and today. We're following a bunch of leads, following up to include or exclude people or vehicles."
Police say the man Gardner-Quinn's friends saw her leaving with is not a suspect in her disappearance.
"No specific suspects have been identified at this time," said Tremblay.
Fliers with her likeness, name and police contact information were posted on utility poles and in campus buildings Monday, and police widened their search beyond the city limits, where officers had canvassed neighborhoods looking for clues or information.
University of Vermont officials sent a campuswide e-mail alert describing Gardner-Quinn and appealing for help finding her, according to spokesman Enrique Corredera.
Friends said they were very worried about Gardner-Quinn, who has gone on exchange programs to Brazil, Costa Rica and South Africa during her time at the university.
"She's not the type of person who would just disappear," friend Tommy Lang told The Burlington Free Press.
Gardner-Quinn was described as 5-foot-8, 135 pounds, with shoulder-length brown hair and a pierced nose. When last seen, she was wearing a gray coat, a green cardigan sweater and a light blue T-shirt.
Fellow students were shaken by her disappearance.
"It's definitely nerve-racking," said Kaitlyn Dillon, 21, of Winchester, Mass. "So many things could've happened."
Jason Walker, a 20-year-old senior from Highgate, Vt., said people were being more cautious about strangers since Gardner-Quinn's disappearance.
"It's a little bit scary," he said. "No one really knows, and that's the scary part. It kind of makes you wonder how safe things really are."