Capt. John Robertson said if the dog is not found the boy may have to undergo anti-rabies vaccination treatment.
The boy was bit on the hand around 10:30 a.m. when he tried to free the dog's leg, which appeared to be stuck from a bench near the intersection of Perkins Street and Shetler Avenue in Napa near the Phillips School, Robinson said.
The small dog has short, thick brown and tan hair. Anyone with information is asked to call the sheriff's department's Animal Services Division at (707) 253-4517.