Think like a predator of a cat. Which ear do you hear the faint meow the most? Go the way you hear the faint meow the most. If it starts getting quieter go the ear it sounds loudest and keep doing it until you get to a place where he might be. If that doesn't work, go get some catmint it might not work though. And wave the catmint everywhere to try and get the kitten to smell it.