The best advice is to look EVERYWHERE. You'd be surprised where they can squeeze into. Hopefully you just have to look in one room.
You can try a few tricks such as placing flour on the ground (if you have hardwood or tile floors) which will give you an indication where the snake traveled to. You can also try to lure him out using a warmed hide as well as soiled rat or mouse shavings.
I haven't had my girl escape (yet) but perhaps leave your snake's water dish and favourite hide on the floor. I've heard a lot of people say that typically snakes won't wander too far from their cage. They also love electronics and such for their warmth.
This is a super stretch, but if you have a camera with video ability, you could set up some sort of "snake surveillance" camera
I truely hope you find your baby, keep us updated!!