A few things you can try are: cats are active at night and early morning, walk around the outside of your house/building and whisper their name, do not shout it, the less yelling and excitement the better and then listen for a meow. They usually don't stray very far from home. Put his food/water, catnip, and clothing you wore earlier in the day in front or in back of your house, they say cats can smell up to a mile. Do not leave the food out overnight as it may attract other animals that can scare the kitty away. Go to your neighbors and let them know your kitty got out and give them your contact info. Walk your neighborhood, shake the treat jar and talk to people as you walk and taclk to your mail carrier. They see lots of animals and if they see a strange Kitty around they may recognize it as yours. Make sure you call local animal shelters, etc. Cats can disappear for days, weeks, months or longer and return so don't give up!