Hasanni, who has cerebral palsy, was reported missing by his foster father, Louis Ross, from the parking lot of the Shuz of Rockridge Shoe store in the 6000 block of College Avenue about 4:15 p.m. on Aug. 10.
Hasanni's foster mother, Jennifer Campbell, works at the store. Ross, Jennifer Campbell, Hasanni and another child lived together in Fremont.
Oakland police and Crime Stoppers initially offered a $10,000 reward for information leading to the whereabouts of Hasanni.
But Oakland police said the Alameda County Board of Supervisors and San Francisco County are contributing another $25,000 each to the reward.
San Francisco Mayor Gavin Newsom said in a statement, "We hope this award will lead to information on the whereabouts of Hasanni Campbell."