(STATELINE, Nev.) -- Investigators say they have new evidence in the search for Alyssa Byrne, the 19-year-old California woman who has not been seen since New Year's Eve.
Byrne's cellphone might have been used after she was last seen close to midnight on New Year's Eve as she attended Snow Globe, a three-day music festival in South Lake Tahoe, Nev., that attracts thousands of people, police said Thursday.
Investigators are still unsure, however, whether the phone was used by Byrne or someone else.
"We have no evidence that there is criminal activity or foul play involved but we are worried for her," Paul Howell, the Douglas County undersheriff, said at a news conference Thursday in Stateline, Nev.
"The nighttime temperatures here are very cold so if she's exposed to the elements, that could be a major concern," he said.
Byrne, of Petaluma, Calif., was last seen by friends around 11:30 p.m. Monday. One friend says Byrne quietly disappeared from her group of friends without saying a word.
"But that New Year's Eve she didn't say a word," said Jay Donnellan, according to local ABC News affiliate KGO-TV. "She basically just left and I called her back and she was on the bus back to the hotel."
Byrne reportedly told friends she was returning to the group's hotel, the Horizon Casino Resort, in Stateline. When Donnellan returned to the hotel around 12:30 a.m., Byrne was not in her room.
"Once we got back to the room, we noticed she wasn't there. We were calling her, back-to-back, sending her text messages," Donnellan told KGO.
It's unclear whether Byrne ever arrived at the hotel after the phone call with Donnellan.
Byrne's family in Petaluma says she has no history of running away.
"My level of hope is that she's out there," her father, Kevin Byrne, said. "Alyssa, if you are, just come home. We miss you."
"Anybody out there that has any information please pick up the phone and call the tip line that's established," he added.
Kevin Byrne has joined search teams in South Lake Tahoe, where police have checked the teen's bank and cellphone records. Police are also scouring surveillance video from nearby hotels.
"I'm waiting for her to come through the doors," her mother, Kim Byrne, said.
Anyone with information is asked to call the Douglas County Secret Witness phone line at (775) 782-7463, or the sheriff's office investigation division at (775) 782-9905.
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