Check carefully around the outside of your house and your neighbors’ houses. Cats don't usually go far initially and they can tuck themselves into unbelievably small and unusual spaces. One person found her cat hiding in the grill on her patio after searching for three days. Go out late at night when it's quiet and call him. Make flyers and post them around your neighborhood with the cat’s picture and your contact info. Post a lost ad on nextdoor.com. Ask your neighbors to check garages, sheds, under decks - anywhere a cat can hide and get shut in. Don’t give up. Good luck!