Sierra LaMar, 15 and Missing; Authorities Fear Kidnapping

Sierra LaMar, 15, has been missing since March 16, and authorizes now believe she could be being held against her will. She was last seen on her way to school but never made it for classes; her parents are asking anyone with information to help.

"The first week, the focus was on the public's help for possible sightings," Santa Clara Sheriff's Office Sgt. Jose Cardoza told ABC News. "Now the focus is to call us with people that are suspicious in the neighborhood. We don't know where she could be in the area, but we are thinking that whoever is involved either lives in the Morgan Hills area or has a familiarity with the area."

So far the search for LaMar has turned up her cell phone and handbag, which had several items of her clothing folded up inside. Over 583 volunteers came out to help locate the missing teen, who lives with her mother and her mother's boyfriend.

Police tracking units were called in to help but lost her scent at the end of her driveway.

"We do not know what she was wearing when she left the house, we don't know when she left the house because no one saw her do it, and we have not had any new credible leads or tips or evidence since discovering the bag of clothes. There have been so many unknowns," Cardoza explained.

Frustration and confusion has only grown as the days continue to pass without any trace of the girl. Police units have searched the wooded areas near LaMar's home, as well as the Calero Lake, which is a popular hangout.

"This seems like a very remote location, and it seems like anybody who would have been there had to have a reason to be there. Therefore, my immediate thought was, 'Whatever happened to Sierra, assuming she did not run away, happened on this block,'" Marc Klaas told the Daily Mail.

Klaas' own 12-year-old daughter was kidnapped and murdered in 1993. He has since organized a missing children's foundation in her name, and the organization is helping with the search for LaMar.

"There are no indications that she would have run away, and no other leads point towards that she would run away," Cardoza told ABC.

Sierra's father, Steve, is a registered sex offender and has been interviewed by police.

"I'm not going to hide it. It is very important they interview me, I get cleared and cooperate with everything," he told the Daily Mail. Police have not named him as a suspect and support his claim of cooperation.

"If there is someone that is holding her, release her," Steve LaMar said on camera. "We don't' care about anything except getting Sierra back home. Just release her, leave her at a gas station, anything, we just want her home."

"We want you to come back home; we know you will find your way back to us," Marlene LaMar, Sierra's mother, said at a candlelight vigil on Friday.