My heart goes out to you. I also have a cat that has been missing since April 22, 2008. He is micro chipped so I still have hope. From everything I have been told and have read it is extremely important that you be proactive in trying to find your cat. Don't just wait for him to return. If he has been gone days now, there is a good chance he is not able to return if he wanted to. Please knock on all your neighbors doors and ask them if you can check their garden sheds and garages, but really look good, because your cat may be getting weak now from no food or water.
I pray that you find him.
xx