Police on Monday were interviewing former and current classmates and searching through a missing Morgan Hill teen's cell phone and laptop computer in hopes of finding clues to her whereabouts.

Over the weekend, the Santa Clara County Sheriff's Department found Sierra Lamar's cellphone not far off the road, in a field about a half-mile from her house.

"We have confirmed that cellphone does belong to Sierra, so we're doing some forensics on that cell phone, trying to get any information we can off that cellphone, as well as her laptop," said Santa Clara County Sheriff's Sgt. Jose Cardoza.

The 15-year-old teenager, born and raised in Fremont, has been missing since Friday morning from her Morgan Hill home.

Lamar's former high school in Fremont, posted her name on a marquee outside the school, and below friends also hung up a missing-person banner.

A group gathered on the campus of Washington High School Monday afternoon in hopes that the missing-person case will have a safe outcome.

"Now that all these days have gone by, we're getting really worried," said friend Jacque Lambiase. "We know she didn't run away, because she's not the kind of person to do that."

Family members released new images Monday of a smiling Lamar.

"She was in an optimistic mood," said Marlene Lamar, the missing teen's mother. "She was very cheerful. She wished me a good day at work. I told her I loved her before she left for school."

Investigators said there is no sign of a crime or that Lamar ran away and are treating it as a missing-person's case.

Police interviewed about 30 students and staff at Sobrato High School Monday, where Lamar transferred in October.

"We have encouraged all of our students if they have any information, even if they don't think it might be very important, to come up and let us know," said Deborah Padilla, principal of Sobrato High School.

Investigators also interviewed friends at Lamar's former high school Washington High School in Fremont, where she was on the cheerleading team.

"I know she's going to come home," said her former teammate McKenzie Lebon. "I don't want to think of anything else other than that."

Friends described Lamar as a happy teen and said most of her close friends were in Fremont. On Monday, friends copied and distributed hundreds of fliers.

"Now we're praying for her to come home and it just makes us so sad," said cheerleading coach Jade Penera.

The Washington High cheerleading squad is heading to regional competition in Southern California next week. They will be wearing ribbons with a zebra pink design – a favorite of Lamar's – in tribute to their missing friend.

"I appreciate all the efforts," Marlene Lamar said. "God bless everyone who's trying to help, even the people that don't know her. I hear they're chipping in and they're trying to help out. God bless you all."

Authorities said Lamar's Facebook and Twitter accounts haven't been used since Thursday and said they have little to go on, which is why they're asking the public for help. Police requested that anyone with information regarding the teen's disappearance get in touch with authorities as soon as possible.