I would look in every nook and cranny, even if it looks too small for your snake to fit. Check inside all furniture, radiators, closets, under doors in other rooms, and I would put some flour on the floor to see if there are any tracks. Try to keep your other pets in a central location so you can see them if you are worried. When is the last time the snake ate?
3 days...
"A Dumb One I May Be, But A Smart One I Must." ~~Josh Emmons.