The parents of a 20-year-old Virginia Tech student who disappeared outside a Metallica concert say they fear their daughter is the victim of foul play but hope for her return.

Morgan Dana Harrington's parents said Tuesday on NBC's "Today" they are devoting all their energies to finding their daughter, who was last seen Oct. 17 outside a University of Virginia arena in Charlottesville.

SLIDESHOW: Virginia Tech Student Disappears at Concert

Dan Harrington called his daughter's disappearance "a parent's worst nightmare."

"Clearly no one ever expects to be in this situation and we have to hold out hope that we're going to see our daughter again."

Harrington, 20, of Roanoke, was attending the concert 10 days ago when she left the arena and was not permitted to return. Her purse and cell phone were found. There was no sign of any type of struggle in the area, state police investigators have said.

Dan Harrington speculated his daughter might have accepted a ride home with someone.

"You know kids at this age think everybody's their friend," said Gil Harrington, Morgan's mother.

Asked if they feared foul play, Gil Harrington, Morgan's mother, responded, "Very worried, very worried. Nothing else makes sense."

Still, she said, they don't want to "fall into survivor's guilt."

"We need to be moving forward and direct all our energies at this point in finding Morgan while people's memories are still fresh," Gil Harrington said.

Police have said they are treating the search as a criminal investigation. They hope a $150,000 reward — including $50,000 chipped in by Metallica — will help generate new leads.

Anyone with information on Morgan's disappearance is asked to call (434) 352-3467.