Start close to the enclosure and circle out gradually. Check under any low laying stuff (couches, chairs etc). If your room is a bit coolish check the warmest darkest places first...

I found mine today hiding in between a frying pan and a lid in our oven drawer after her night out (only about 17 feet from her tub)... So be thorough We were lucky, five minutes of looking....

If you have hardwood try spreading out some flour, or setting up a warm hide somewhere for him. Even try leaving out a FT rat or something.