I understand your panic, I am just like you if one of them doesn't come home.
But, usually, they just like the spring weather and don't feel like going home, or they got themselves locked in a garage or garden shed.
If he hasn't turned up by sunset, wait till it is dark and quiet, and take a walk. Call his name, then wait, walk on, just a few doors, then call again. Walk as close to the sheds and gaqrages as you can, so you will hear his call IF he is in there. Bring a good pic, and show it to people you meet in the street, especially dog owners. They often see a cat rush out of or into the bushes when their dog passes, so if he is around, there is a fair chance a dog will have flushed him out at one time.
When Tosca was missing I put up flyers with her photo and my cell phone number, and I got a call from a nurse cycling home from the nursing home, late at night. She had seen her strolling in the park.