Usually they're close by. But they can squeeze themselves flat and get under doorways you think they can't. Is he a climber, or does he always head for the floor? Ball pythons that like to climb will tend to find hiding spaces higher up; ball pythons that don't like to climb will tend to find spaces on or near the floor. They hide in closets, under cabinets, between the backs of books and the bookshelf, in drawers, and in the tight space between our expandable dining room table and the wooden leaf that we keep stored underneath the table top. The best one was a snake that found an open hole in the back of a stereo speaker, crawled in and took a nap while I panicked for 4 hours straight.

If you can't find him by nightfall, turn all the lights out and wait quietly for a 1/2 hour. Then start in the room you lost him in, and go around the house tiptoeing and listening. Listen in each room for 5 or 10 minutes. They're not actually silent--you can hear them crawling and bumping around. (That's how I found the one in the closet.)