I feel for you. My sister left the upstairs window open when she took the ac unit out and my youngest cat got out. She was only around two years old, small for her age, always an inside cat. I walked my neighborhood and the woods with a flashlight every night for a month. Around 2-4am is supposed to be the best time to look. Try leaving some of your old clothes out on your porch, near the door, try some of his cat litter. Ask neighbors to check their sheds and garages. Go outside and shake some dry cat food or something that sounds similar like a box of rice or pasta. Post on craigslist, social media. Go to the local shelters, animal controls, and vets with fliers, make sure to include a good picture. I never found my Baby Kitty . I still cry and feel terrible that I wasn't there to protect her. I saw foxes and she wouldn't have known any better to be afraid of them. Not even a month after I stopped looking, my oldest cat that I had had since I was ten died unexpectedly. I really hope you find him .