Look everywhere! In nooks and crannies, especially anywhere warm. Check sofas, cushions, boxes, anything your snake could hide in.
If you have no luck try a few traps. Corn snakes mostly move round at night, so try leaving something rustly out, like a plastic bag, around the edge of skirting boards etc. Another trick I've heard about is to put down flour to look for tracks the next morning so you can get an idea of where it is moving around.
Don't try putting down sticky tape to trap your snake, it can cause serious injury when you attempt to remove it!
Lastly you could try putting a warm (so the snake can smell it) dead mouse out in a hide on the floor to see if you can tempt your snake out that way.
Them's my suggestions (all heard from other more wise-type snake folks than me
)
Stubby