Go around the neighborhood. I assume she's an indoor/outdoor cat. Ask your neighbors to check ALL their open spaces, garages, sheds, etc. My friend's cat went missing and she found him enclosed in someone's shed. Put up posters. Look in any crawl spaces you have. I lost a cat that fell out of my living room window down 2 stories. He was missing for 5 days (he was semi-feral). I came home from work one day and saw in sitting in the back yard. When I went to get him, he ran into the crawl space of my apts. That's where he had been the whole time. Cats do not stray far from their food source. There is also the factor of elements, coyotes, weather, etc.

Any way you can borrow a trap and set it for him?? If he's hungry enough and hasn't eaten for a while, he should be fairly easy to catch.