Alyssa Byrne Found Dead: California Teen Disappeared New Year's Eve (UPDATED)

Police are hopeful that activity on a missing Petaluma, Calif. teen's cellphone could help find her.

ABC News reports that Alyssa Byrne has been missing since New Year's Eve when she left Snow Globe, a three-day music festival in South Lake Tahoe, Nev.

UPDATE: Byrne was found dead on Friday, according to the San Francisco Chronicle. Original story continues below

Investigators said the phone was used after the 19-year-old disappeared, but they don't know if it was Byrne or someone else who used it.

Cops are also trying to determine whether any information can be gleaned from cryptic tweets sent out on an account believed to be Byrne's.

One tweet sent on the night Byrne disappeared said, "Just lost all my trust in the person I trusted most." Another reads, "After tonight you'll never be apart of my life you won't be a memory of 2013 a new year you'll never be apart your nothing to me."

Byrne's friends told the Mercury News that she wasn't acting like herself when she abruptly decided to leave the festival an hour before midnight. She also passed on a chance to visit with old high school friends at her hotel.

Micah Alex, the last friend to see her, told the paper Byrne was likely intoxicated when she greeted him with a hug that night.

"She just seemed like something was wrong with her, like she wasn't all there, you know?" Alex said.

Paul Howell, the Douglas County undersheriff, said there's no evidence of criminal activity involved in Byrne's disappearance.

Byrne's mother Kim Byrne told the San Francisco Chronicle her daughter had never gone missing before and she didn't know where she could be.

"We just have no idea," Kim Byrne said. "That's the million-dollar question."

A reward of up to $1,000 is being offered for information that leads to Byrne's whereabouts. Anyone with information should call South Lake Tahoe police at (775) 782-9905.