check everywhere even if you think its impossable and if you cant find him try running a rat across the edge of the wall next to the floor to scent it then place the rat in a hide on the floor to try and lure him out, sprinkle flour on the floor (if its wooden lol) to see if you can see any tracks give it about an hour with the lights off in the room and the door closed. not my ideas and i'll give credit where its due but i cant remember who posted these first.
good luck finding him