Police say the unprovoked attack happened on May 2 near Dundas Street West and Augusta Avenue, just south of Kensington Market.
Const. Jennifferjit Sidhu said the boy sustained injuries to the back of his head, his eye and has lacerations on his face.
"They're non-life threatening and he's been released from hospital, but he's still very shaken up," Sidhu said.
Police are looking for a black man in his 20s, who's approximately 5'10", has a medium build, short black hair and is unshaven. They say he was last seen wearing a plastic Spider-Man mask on top of his head, a long-sleeve shirt, black jeans, and was carrying a skateboard.
Anyone with information is asked to contact police at 416-808-1400.