Fairfield police investigators were on the streets early Sunday canvassing the neighborhood near the park where a 13-year-old girl was found dead, a police spokesman said.

Officers were interviewing neighbors as they tried to track down leads in the search for the girl's killer, while investigators were asking for the public's help with any information that would help them determine the whereabouts of the girl after she disappeared Thursday and was found dead Friday, said Officer Cleo Mayoral, a department spokesman.

"If anybody knew anything, or saw anything, we are asking them to give us a call," Mayoral told The Associated Press.

A passerby discovered the girl's naked body a little before 7 a.m. Friday in the city's Alan Witt Park and flagged down a police officer who was driving by, Mayoral said.

An autopsy was performed and police have not yet said how the girl died or released the girl's name.

The girl was reported missing around 5:45 p.m. Thursday by her guardian at a foster home in nearby Suisun City. That city's police Cmdr. Tim Mattos told the Daily Republic that the guardian last saw her board a school bus. He said she was in class all day and was expected home around 4 p.m.

He called the discovery of the dead child "a shock to our system."

Sacramento television station CBS13 reported the girl attended Green Valley Middle School, which is about eight miles from the park.

School Principal Gregg Hubbs declined to comment on the girl's death.