An autopsy was scheduled Wednesday on an unidentified body found several miles from where a 17-year-old Southern California girl disappeared on her way home from a summer school class last week.

Riverside County sheriff's Deputy Melissa Nieburger said investigators were proceeding cautiously and wouldn't be able to positively identify the remains for possibly several days.

A resident reported finding human remains Tuesday near an empty stretch of road lined with utility poles and desert scrub.

Hours earlier, the family of 17-year-old Norma Lopez pleaded for her return and authorities offered a $35,000 reward for information after efforts to find her stalled.

"If the person that took her is out there, please let her go," sister Elizabeth Lopez told a news conference. "She hasn't done anything to anyone to deserve this, at all."

Norma Lopez vanished Thursday on her way home from a summer class at Valley View High School in Moreno Valley, in the inland region east of Los Angeles.

Deputies found personal items and signs of a struggle in a field the girl often used as a shortcut home. Police went door-to-door, and searchers using dogs combed the areas for days.

Borja said investigators haven't identified any suspects or persons of interest and are presuming the girl was kidnapped.

"We contacted every friend, relative, everybody available that we can and there's no information that would leave us to believe that she's a runaway," he said.

FBI investigators have talked to school friends and other acquaintances, said Don Roberts, the FBI's supervisory special agent in Riverside.

"We have our own children, and it does not take much motivation for FBI agents and police officers to work day and night, as we are, to look for Norma and find clues that will lead to her recovery," Roberts said.

Borja urged the public to report suspicious strangers.

"We're following up all leads, especially when it pertains to, you know, deviant behavior or behavior that's not normal toward young females," he said.