Angelo Epassa, 4, boarded a bus in the Humberwood Boulevard and Kingsplate Crescent area at 8:15 a.m., police said.
The boy has a brown complexion and stands between three-foot-five and four feet tall.
He was wearing a white, hoodie pullover, dark-blue pants, a white shirt, as well as a blue-and-black winter jacket, a green-and-blue balaclava-style hat and a Spider-Man backpack.
Anyone with information about Angelo's whereabouts is asked to contact police at 416-808-2300. Tips can also be passed to police through Crime Stoppers at 416-222-8477.