MORGAN HILL (KCBS) – Detectives investigating the disappearance of 15-year-old Sierra LaMar now believe the Morgan Hill teenager was likely abducted, the Santa Clara County Sheriff’s Office announced Tuesday afternoon.

After interviewing those who know her best, investigators believe it is highly unlikely that Sierra, who went missing a week and a half ago, ran away from home, sheriff’s spokesman Sgt. Jose Cardoza said.

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The sheriff’s office is asking local residents to report any suspicious behavior they observe in co-workers, neighbors or other community members.

Such activity could include changing one’s appearance, cleaning a vehicle in an extreme way, missing days of work, or showing an unusual interest in or avoidance of news reports on the case, Cardoza said.

KCBS’ Chris Filippi Reports:

Tuesday morning, hundreds of volunteers from throughout the Bay Area showed up at Burnett Elementary School in Morgan Hill to participate in an organized search for Sierra.

The KlaasKids Foundation, which provides search-and-rescue services for families of missing people, was on hand to manage the search.

By 9 a.m., more than 200 people had registered to help look for Sierra and provide administrative support for the effort, KlaasKids founder Mark Klaas said.

A dive team and cadaver dog search the Calero Reservoir near Morgan Hill for clues to the disappearance of Sierra LaMar. (CBS)

Also Tuesday, a dive team and cadaver dog searched the Calero Reservoir near Morgan Hill, according to CBS 5’s Len Ramirez.

Klaas has been encouraging the 15-year-old girl’s family not to give up even though she has not been seen since March 16 when she left home to catch the school bus.

“People always have to remember that, as bleak as things can look, there are the Elizabeth Smarts, the JC Dugards and the Missy Sanchezes out there who, over some period of time, do come home and are able to put their lives back on the right track,” he said.

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KCBS’ Matt Bigler Reports:

Klaas’ 12-year-old daughter Polly Klaas was kidnapped from her Petaluma home in 1993. Searchers looked for Polly for about two months before police arrested a suspect in the case, Richard Allen Davis, who led them to her body. Davis was later convicted of her murder.The case spurred California lawmakers to adopt the three strikes law.

The foundation announced it would supervise a series of searches this week, rain or shine, after police efforts over the weekend yielded no new clues to Sierra’s whereabouts. Klaas said all volunteers are at least 18 years old and present valid identification to participate.

A spokesman for the Santa Clara County Sheriff’s Department said authorities are still investigating sightings and other tips, and have so far not found any evidence of foul play. Police have begun re-interviewing friends and classmates for new leads.

The last significant break came more than a week ago when authorities found Sierra’s Juicy purse with clothing she may have worn before it was tossed near an intersection.

One of the volunteers, Michael Le, understood only too well what may be at stake as the days stretch into weeks. His sister Michelle Le, a nursing student, was found dead by a volunteer after her high profile disappearance. KlaasKids helped in the search for Le.

“I wanted to do something to pay it forward and be able to do the same for another missing person’s family the way they helped us,” Michael Le said this morning.

Le said the Sierra LaMar case was eerily reminiscent of what his family went through when Michelle disappeared. The woman accused of murdering her will stand trial in September.

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