Have you noticed anyone pay extra attention to Obie before he disappeared? Anyone in the neighbourhood, while out walking? Do you have neighbours that you don't talk to much, or ones that are not very friendly,strange in some way?
Sorry I'm not pointing the finger at anyone but just brainstorming for what else you could do, also
I once knew someone that used to breed American Staffords. Someone stole a whole litter of pups, ended up being a neighbour.