Tear the place apart if you can. Look absolutely everywhere, whether you think the snake can get into them or not. If that doesn't work you can put out a food item and wait and see if it comes out to eat it. Put flour on the floor and see if his movement makes tracks in it which you may be able to follow. Put tin cans behind furniture that he may knock over alerting you to his presence. Let us know if you find him.

Hope that helps
Mike