OAKLAND, Calif. -- Volunteers trying to find a 5-year-old Oakland boy who's been missing for more than three months are hoping a $75,000 reward will bring some fresh leads to the case.

They've held a number of vigils for Hasanni Campbell since he was reported missing Aug. 10, but they say the latest one Tuesday had a poor turnout. Authorities and volunteers have now raised the reward, up from the $60,000 announced in September.

Hasanni, who has cerebral palsy, reportedly went missing when his foster father, Louis Ross, briefly left him alone in a parked car in the city's Rockridge neighborhood.

Police initially arrested Ross and his fiancee, Jennifer Campbell, on suspicion of murder, but prosecutors declined to file charges due to lack of evidence. Authorities say searches have turned up no significant leads in the case.