How old is the building you're in? Are there holes in the walls/floors that the snake could get into? If so.. this could get a lot tougher (ps.. AFTER you find the snake.. block as many as you can if you do).
If not, remember when your snake is most active-- it is usually just after lights out. Set some "traps" (plastic bags that will make noise when a snake passes) along walls and such. Turn out the lights at like 9 at night, and just listen. Leaving baby powder or corn starch in doorways can tell you where they are going. I've also heard people recommend Putting a meal and a warm hide in the corner of a likely room.
Good luck! A snake that young is tough to find. Be sure to seal up the enclosure better once found.