Have you contacted the Toronto Humane Society and informed them he went missing? Since he was a surrender they should have his previous address on file and can check that neighbourhood as animals sometimes try to head back to their previous homes.
Have you taken the dog on a slow stroll around the building especially where your balcony faces to see if s/he notices any interesting/familiar scents?
Some of these may only work with a house deck but I'll post them all anyways:
If you can put his litterbox and/or a worn but unwashed t shirt or pair of smelly shoes of yours out on the deck this may help lead him home
Go around the neighbourhood at dusk/dawn calling him, rattling a treat container or tap a spoon on his dish or tin of food. Bring a flashlight to pick up the shine off his eyes from under cars/decks/bushes or up trees.
If you can poster the neighbourhood, plus leave one w/ local businesses, schools, pet supply stores, grocery stores, bus stops, vets & all animal shelters in the area that will help garner attention that this kitty has a home who wants him back
Please visit the animal shelters in person often times the shelters are understaffed/over worked with so many animals/requests etc they may not have the time to personally look into each phone call or an emergency/something comes up in the meantime & the request gets overlooked.
Going in person means you can visit & identify the cat right away, if an animal comes in terrified it may act out of character & be labeled as sick or a feral and not be placed with the general population please ask to see these areas as well.
Good luck &