I don't mean for this to sound like an insult, but are you certain that the snake isn't in an odd spot in his viv? More than one person has thought they had an escapee when what they had was an excellent hider in an unusual spot in the viv. Small holes in viv decor items can serve as unintentional hides.
If he's really out, be calm and follow the recommendations given. Do a search for other recommendations, like putting the viv on its side against the wall, baiting him, or building a funnel trap with a 2-L bottle. Odds are good that you'll find your snake in the same room as the viv if you act fast (24 hours or so).
Best of luck.