Imani Howell, of San Francisco, was reunited with her family at 2 p.m., police said. Her parents found her in San Francisco on Third Street and Evans Avenue on a Muni vehicle and took her home, where police were notified.
Police said the girl is in good condition and is being interviewed by investigators.
Howell left for school on Nov. 10, but never returned home that day. She was seen a week later on International Boulevard in Oakland, an area known for sex trafficking, according to police.
Officer Albie Esparza said people had reported seeing Howell several times in San Francisco and Oakland during the time she was missing.
Oakland police spokeswoman Johnna Watson said they were concerned about the possibility that she had become a victim of sex trafficking.
Police said the investigation into her disappearance is still ongoing and asked anyone with information about the case to contact San Francisco police anonymously at (415) 575-4444.