Keep checking secluded spots, garages , bats, under vehicles. One of mine (indoor) hid 5 days in a neighbor’s bat. Had looked there several times.
Put out his litter box, smelly food, pieces of your clothing.
Make a chum trail with used litter or wet food in a gallon of warm water.
Go out at night with a flashlight and call him.
Go repeatedly, especially late at night.
Alert shelters, rescue groups , groups that feed feral colonies, vets.
Prayers he is soon home and safely inside.