By Paul Payne and Mary Callahan, Press Democrat

STATELINE — Law enforcement officials in Nevada and South Lake Tahoe expanded their search Thursday for a missing Petaluma woman, combing the snowy region by air and land, conducting a room-to-room sweep of her hotel and poring over her cellphone activity.

But so far, there has been no sign of Alyssa Byrne, 19, who vanished New Year’s Eve while attending a three-day music festival at Lake Tahoe Community College.

The aerial search will resume this morning with help from an additional helicopter from Reno, Douglas County Undersheriff Paul Howell said in a news conference.

Alyssa Byrne

He stressed the importance of finding Byrne soon because of the below-freezing overnight temperatures in the ski resort area.

“We’re concerned,” he said. “And we’re putting every resource we have into it.”

Howell said the last activity from Byrne’s cell phone was recorded at 12:03am Jan. 1, or about 10 minutes later than previously thought.

One message on her Twitter account read, “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.”

The last message was, “Just lost trust in the person I trusted most.”

But Undersheriff Paul Howell cautioned, “We’ve seen those, and there’s still a debate as to the actual author of those tweets.”

Howell added, “Since that time, the phone has gone inactive.”

He cautioned that activity on her phone wouldn’t necessarily pinpoint her location — just her phone’s.

The Rescue Coordination Center at Tyndall Air Force Base in Florida is examining the cell activity, Howell said.

The FBI and search and rescue officials from Nevada and California also joined the search, as have those from the National Center for Missing and Exploited Children.

Sheriff’s deputies were in Petaluma interviewing acquaintances.

Howell said authorities were doing a “room-to-room search” of the Horizon casino in Stateline, where Byrne and her friends were staying.

Security officers at the Horizon and other casinos are going through their security footage, Howell said.

Friends and family blanketed the South Lake Tahoe area with fliers describing the missing woman and urging anyone with information to call authorities.

Her father, Kevin Byrne, drove to Stateline on Wednesday to help find his daughter. He said Thursday he was optimistic since police “didn’t find her body in the snow.”

“When this is all said and done and we get her back home, then we’ll have a nice party,” he said Thursday night while seated near the Horizon resort lobby.

“Maybe she partied harder than normal,” he said. “I don’t know.”

Concerns for Byrne’s safety were mounting Thursday amid a sense that something wasn’t right with her in the hours before she disappeared.

Friends who saw her shortly before she went missing said she wasn’t acting quite herself when she unexpectedly left a New Year’s Eve concert an hour before midnight and, later, passed on a chance to visit with old high school friends at her hotel in the wee hours of New Year’s Day.

Douglas County sheriff’s Sgt. Pat Brooks said people often go missing at Tahoe without so much ado, but single-digit temperatures made it imperative Byrne be found, he said.

Investigators said they had no leads as of Thursday evening.

A reward was being offered in hopes someone would come forward with information, even confidentially.

Byrne lives with her mother and father in Petaluma. She works as a hostess at the Cattlemens restaurant in Petaluma and attends Santa Rosa Junior College. Her plan is to become a paramedic-firefighter, according to her mother, Kim Miller-Byrne.

Last Saturday, Alyssa Byrne and friend Jay Donnellan, a high school classmate, and two other friends from Napa drove to South Lake Tahoe for the outdoor SnowGlobe Music Festival, a three-day event on the community college campus that began Saturday afternoon.

The four shared a room at the Horizon, and spent most of the ensuing days together, shuttling between their hotel and the festival, Donnellan said.

Monday night, New Year’s Eve, they were outdoors at the festival about 11pm when Byrne got slightly ahead of her friends as they made their way through the crowd and then, suddenly, disappeared, Donnellan said.

Byrne had left a bit earlier than her friends a night earlier, after falling in a puddle and getting wet enough that the outdoor temperature was unbearable, he said.

But it was odd for her to leave without saying anything or even alerting them she planned to go, Donnellan said.

But Byrne called his cell phone twice. He missed the first call, but about 11:30pm she got through to him, saying she was on a shuttle bus back to the Horizon, he said.

About 20 minutes later, her friends tried to leave the event, but were held up by midnight fireworks and crowds in the street that delayed their return to the hotel until about 12:30am.

When Byrne wasn’t in the hotel room they shared, Donnellan called her cell phone, but it went unanswered — as it would each of the 10 or 15 times he called that night, until it began going straight to voicemail the next day.

That night, sometime between 12:30 and 1am Jan. 1, Alex — who was among several groups of young people from Petaluma attending the festival — crossed paths with Byrne in a passageway between the Horizon lobby and a bar. She had put her hair in a pony tail and was wearing a black sweatshirt, not the heavy, white winter jacket she had had on earlier at the festival.

They hugged and exchanged greetings, but she didn’t seem herself, Alex said, and showed no interest in visiting with his girlfriend, a close high school friend, or several other classmates with them.

Usually very social, she “was just kind of in her own little world,” Alex said. “That was the last time we saw her.”

Donnellan said he was not aware of her having consumed anything besides beer, but Alex said she appeared to be under the influence of drugs or alcohol, and clearly would have been too impaired to drive.

Alex was among those with whom Donnellan talked that night as the hours went by and he and his friends were unable to locate Byrne.

Donnellan and the others in their traveling party went out until about 5:30am, in part enjoying the evening and in part looking for Byrne. Two other friends stayed back at the hotel room in case she returned, he said.

Donnellan said he figured, at the time, Byrne might have gone off with a girlfriend, though she’d made no mention of meeting anyone new or running into someone the others weren’t aware of.

He said his friend is strong and smart enough to take care of herself, and would never “wander off with some random guy.”

“It was almost like she was ignoring our phone calls for some reason. I mean, I don’t know — like she was meeting up with somebody (and) she didn’t want us to know where she was going. I don’t know.”

By morning, conversations between friends and Byrne’s father had intensified as they struggled for answers.

Donnellan and the others delayed their departure from the Horizon — until security was about to kick them out, he said — as they checked with other hotels, hospitals, the jail, the sheriff’s office and any other place they could think of, Donnellan said.

They filed a missing person report with the South Lake Tahoe Police Department. The case was then referred to the sheriff’s office in Douglas County in which the Horizon is located.

Kevin Byrne said he’s been impressed with the work of both departments and has a cadre of friends and relatives working with him to distribute fliers about his daughter’s disappearance. Thursday, he was fielding multiple calls from media outlets around the nation interested in the story.

He was at the sheriff’s office until midnight Wednesday as investigators combed through Horizon surveillance tape in an unsuccessful search for images of Byrne, and again on Thursday morning, while a search and rescue effort was organized on his daughter’s behalf.

Alyssa Byrne is described as 5-feet-3-inches tall, weighing about 125 pounds with fair skin, dyed black hair and blue eyes. She was last seen wearing a black sweat shirt, black snow boots and black yoga-type pants, with her hair pulled back.

Anyone with information about her is asked to contact Douglas County at (775) 782.5126, Investigator Dennis Slater at (775) 586.7255 or an anonymous tip line at (775) 782.CRIME.