If you can sit outside and talk in normal voices, especially late at night, that can provide an opportunity for him to return. Lost cats usually hide out and don't respond to calling. Lost cats also tend to come out really late at night (like 3:00 or 4:00 in the morning) when everything is quiet. Talking in normal voices will cue a cat in to the fact that it might be safe to come out.
If you have anything with his scent on it (pillow bed or whatever), putting that outside your door can help too. Cats have extremely sensitive smell and tend to identify "home" with odors -- especially their own.
We went through this last month when I inadvertently locked our indoor cat outside. We searched the next day, but it wasn't until dusk when my dd and I were out on the screen porch talking about her that she finally showed up. I read about a dozen articles online about how to find a cat, and the best tips were the above -- night time, scent, and ordinary conversational voices.