Theres about a million places it could be, make sure you check in small dark places, they can squeeze in places a lot smaller than you think. When my snake got loose it cralwed into the closet and was hiding under a pile of clothes. Also look high, I've heard lots of people have found theirs around the top of windows, between dressers and the wall and places like that.
You could also do a seach on this sight, there are lots of posts with good ideas about finding snakes.