Since news spread on Facebook that , the community has responded with an outpouring of support online and in person as volunteers from throughout the Bay Area join the search for her.
A team of about 60 law enforcement officials from a number of agencies are combing beaches, trails, water and bluff areas in the Marin Headlands, Ocean Beach and Land's End in San Francisco, using horses, helicopters and boats. They recently expanded the search to parts of the city.
After discussions with Allison's family, Danville Police Chief Steve Simpkins said Allison is considered at-risk and that the case is "absolutely not criminal, it's a personal matter."
About 100 friends, family members and volunteers from Danville headed to the city as early as 4:45 a.m. Tuesday, when word spread that Bayliss' bike had been found in a parking lot near the Golden Gate Bridge.
Simpkins said the participation of Danville residents in the search has been awe inspiring.
"The community of Danville is acting as if it's their own family member," he said.
Troy Corti, a 2002 graduate of , is part of the volunteer effort.
Corti, who grew up in the San Ramon Valley but now lives in San Francisco, heard about Bayliss from text messages and Facebook.
"I thought it (volunteering) was something I should do," he said.
Corti said the effort exemplifies the strong sense of community in the Danville area.
"It says a lot about the San Ramon Valley community," he said. "Everyone is trying to do whatever they can to help. Even those who can't make it out there are doing their part."
Once it is dark, authorities have to start worrying about the safety of the searchers, said Simpkins, who has been in San Francisco helping with the search since Tuesday morning.
Authorities and family members are waiting in Danville should Allison return home, Simpkins added.
Find Alliy Bayliss, a Facebook page created Monday night for the search, had grown to more than 9,000 supporters by Tuesday afternoon. The page is serving as a message board for people to share their prayers and other thoughts, as well as to relay information for people wanting to help in the search or get updates.
Bayliss was last seen at San Ramon Valley High on Monday morning, and police have said she may be at risk of harming herself.
Her black and purple Diamondback mountain bike was found chained to a bike rack in a parking lot at Fort Point near the Golden Gate Bridge early Tuesday.
She was last seen wearing a red zip-up hoodie jacket, jeans and mismatching flip-flops, one green and one yellow. She is 5-foot-8, has blue eyes and blonde hair and weighs 130 pounds (see photo).
If you want to help:
National Park officials said they no longer need people to search in the areas near the Golden Gate Bridge. People can help with the search in other parts of San Francisco.
Volunteers can go to the command post on Lincoln Boulevard in San Francisco. The nearest cross street is Armistead Road, near the entrance to the Golden Gate Bridge. For more information, call John at 925-480-7780.
Bay City News contributed to this report.