They usually don't go far if they're indoor only cats, especially. Look in nearby garages. Do you have a neighbor who only goes out once in awhile? Look in basements, and hallways/ front foyers. Do you have drain ditches? He may be in there. Look under dense shrubbery. Use a long stick and look underneath them. Depending on their height of fear, you can figure out how far he went. The really scared ones will dive into the first dark quiet spot they find. Some may wander around sniffing for food or a friendly human. Put out some stinky fish. You can add hot water to make it smell more ripe . Also, if there's not much wind, put out a catnip trail. I've caught more with catnip, than anything else. Walk up and down your nearby alleys, calling. Sometimes they're howling, but no one hears them. Seriously check your surrounding area. They're usually in a one block radius.