An 11-year-old Mississauga boy who failed to return home from school Monday, sparking a large search that lasted up to 16 hours, was found in good health Tuesday at a Toronto building where his family used to live, police say.

Police wouldn't identify the location where Shaundrey Knight-Bryce was found or where he spent the night, but they say he was asleep and "not in the care of anyone" when he was located.

Officers found the boy after Toronto police received a tip from a citizen who saw him in the building and then saw a news report about the disappearance.

Knight-Bryce was in good health, although he hadn't eaten for some time, said Peel Regional Police spokeswoman Const. Fiona Thivierge.

He was reunited with his grandparents, who live in the area where he was found, and they were taking him to his mother, Thivierge told reporters.

Police are looking into how the boy wound up at the building.

Earlier Tuesday, police said the boy was last seen by friends as he left Darcel Avenue Senior Public School between 3 p.m. and 3:30 p.m. Monday.

At the time, Knight-Bryce was walking alone and he was heading in the direction of the family's home, but he failed to arrive, police said.

His mother contacted family and friends and she conducted her own search before notifying police at about 9 p.m. She last saw him that morning when he left their Goreway Drive residence to walk to school.

Before Knight-Bryce was located, Thivierge said there was no indication of any problems at home or at school and his disappearance was out of character.

Thivierge said the boy's family was upset and getting "very nervous."

"I’m sure they’re as stressed as we are, worried about this little boy’s safety," she told reporters before he was located.

Thivierge urged people to be on the lookout for the boy in Mississauga and near Jane Street and Finch Avenue West in Toronto, where the family lived before moving about a year ago.

“This is one of those calls where anybody who’s a parent hears that an 11-year-old boy is missing and our heart kind of clenches,” she said. “This is something where the entire community will be upset and concerned for this boy’s safety."

Command post set up at mall

Police set up a command post at Westwood Mall on Goreway Drive, north of Derry Road East, to co-ordinate the search, and officers went door to door to ask people if they saw the Grade 6 student.

A canine unit was brought in to try to track the boy's movements.

Police also visited businesses to take a look at surveillance video.