Get a photo and do some signs around the neighbourhood, call the local pound, all the local vets and any shelters eg, rspca etc. My dog was missing for a few days and I kept doing the rounds and we eventually found her about a week later. She had caught a train to the city and then another one out to the end of the line so she was about 25km from home. She had slipped her collar and had no microchip - fortunately someone had her and reported her. I hope you find him It's just so worrying when you don't know ehere they are!