I did the same as Cheekychops - Monty went out one morning & didn't come home for breakfast, still didn't come back that night & I went into a complete panic. Posters everywhere, phoned the vet, local animal sanctuary, everyone! Searched all over, called him - no response. Went to work the next day, feeling really upset (cried on the phone to a couple of people too). Then....when I got home that afternoon, the little monkey was sitting on the stairs as though nothing had happened. (I left the cat flap open for him).
Ask people to check their sheds &c, just in case he's been shut in somewhere. I do hope he turns up. Let us know, won't you? K xx