Authorities investigating the disappearance of a California girl searched underwater Thursday after sonar images taken earlier this week detected suspicious objects in a local reservoir.

Sierra LaMar, 15, was last seen early March 16 leaving her Morgan Hill home to walk to a school bus stop.

Divers from the Santa Clara Sheriff's Office began searching the Chesbro Reservoir Thursday after sonar pictures detected areas of concern, Fox affiliate KTVU-TV reported. 

"Based on the size and shape and shadowing that we're seeing from the side scan sonar, we'd just like to go back and take a second look at them," Santa Clara County sheriff's Lt. Dan Rodriguez said. "They are larger than normal objects."

The search of local reservoirs, including Chesbro Reservoir and Uvas Reservoir, will continue on Friday, authorities said. 

Investigators have said that they think LaMar, a sophomore at Sobrato High School, was likely the victim of an acquaintance abduction.

The girl's cell phone was recovered shortly after her disappearance about three-quarters of a mile from her home after police tracked its electronic ping. Police said the last text LaMar sent out was shortly before 7 a.m. the day she disappeared, and it was not a distress text.

The girl's bag also was discovered a couple of miles from her home. A pair of her pants and shirt were found neatly folded inside the Juicy brand bag.

Sierra lives with her mother and stepfather. She transferred to the school in October after the family moved from Fremont to Morgan Hill. 

The girl's father, Steve LaMar, who lives some 40 miles away in Fremont, is a registered sex crimes offender but is not considered a suspect in the case.

Sierra LaMar is described as 5 feet, 2 inches tall with brown hair. She was last seen carrying the 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