Police say Emilliano Terry disappeared after his mother briefly turned her attention away from him at Kasuth Park on the city's east side Sunday afternoon.
Police initially were told he may have gotten into a black car, possibly a Saab. Tracker dogs were brought in Sunday night to try to pick up his scent.
Emilliano's mother, 20-year-old Camilia Terry, told police she was tending to one of her other children and when she looked up, Emilliano was gone.
Officers are searching the park and canvassing a nearby neighborhood. During the night, the volunteer group Guardian Angels spent several hours searching abandoned homes, garages and commuter train stops.
Emilliano was wearing a gray North Face coat, a red and black sweater, blue jeans and blue and black Champion tennis shoes.
Anyone with information should immediately call Cleveland's Fourth District Detective Bureau (216) 623-5418.