Updated

Investigators are poring over computer and cellphone records of a missing California girl in their search for the teen who was last seen early Friday walking to a school bus stop.

Authorities on Monday said they found the cellphone belonging to 15-year-old Sierra LaMar in a field not far from her home in Morgan Hill, Calif., about 25 miles south of San Jose in Santa Clara County.

Fox affiliate KTVU-TV reported Tuesday that police are now examining the phone, a Droid smartphone, as well as the girl's laptop computer, for any clues into her whereabouts.

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

Police found the phone Saturday night about three quarters of a mile from LaMar's home by tracking its electronic ping. It was discovered about 20 feet from the side of the road that LaMar used to walk to her bus stop.

More On This...

    The girl was last seen leaving for school Friday morning. Police dogs searching for the girl lost her scent at the driveway of her home, according to the station.

    The teenager usually walked from her home to a nearby bus stop, but a bus driver reportedly said he saw no sign of her.

    Investigators have since scoured creek beds and fields in the area, looking for any trace of the girl. Authorities have also interviewed 30 students and faculty members at Sobrato High School, where LaMar recently transferred from another school.

    The girl was born and raised in Fremont, Calif., and had attended Washington High School, where she was a cheerleader, before the family relocated to Morgan Hill, KTVU reported.

    On Tuesday, the teen's mother, Marlene LaMar, pleaded for her daughter's safe return, telling the Morgan Hill Times that "I want her home, we love you so much, we really miss you.

    "If there's somebody out there that knows where she is, or is holding her against her will, please find it in their heart to let her go and let her come home to us," she told the newspaper.

    Authorities are treating her disappearance as a missing persons case, but family and friends of the girl say it's unlikely she ran away. The girl's cellphone charger was also found in her bedroom and her Twitter and Facebook accounts haven't been used since Thursday, leading many to believe she did not plan her disappearance.

    "She's always in contact with family and friends. She wouldn't leave everyone out of the loop," her sister, Danielle LaMar, told the station.

    Sierra LaMar is described as 5-feet, 2 inches tall, with brown hair. She was last seen carrying a Juicy brand pink and black purse.

    Anyone with information on the teenager's whereabouts is being urged to call the Santa Clara County Sheriff's Department at (408) 299-2311.

    Click for more on this story from KTVU.com