Authorities don't know whether 20-year-old Morgan Dana Harrington is alive or whether "she has met some kind of ill fate," Virginia State Police Lt. Joe Rader said.
Rader told a news conference in Charlottesville that police have received more than 100 tips from around the country.
A passer-by found her purse and cell phone between the arena and an athletic field at UVA, Rader said.
Police planned to conclude their ground search Wednesday. They halted an air search earlier.
The family plans to offer a reward of at least $50,000, according to police.