Put up flyers everywhere asap. It will help a lot. Be sure to tell people to take a picture of the flyer so they’ll have your phone number too. Also people put their dirty laundry outside for the scent of home
Indoor cats rarely go far. One of mine hid 5 days in a neighbor's basement. Had looked there several times.
Keep checking garages,sheds,basements,secluded spots,under porches and vehicles.
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.
Get a humane trap.
Alert shelters,rescue groups,groups that feed feral colonies,vets.
Prayers he is soon home and safely inside.