I set a trap last night around mealtime, and the injured cat walked right past it! Sure enough, by morning I'd caught a young raccoon. I released the mad baby coon far away from home and came back to re-set the trap in a slightly different place. Hopefully, the coons will be sleeping during the day, and with some Divine intervention, maybe I'll get the right cat. At least he/she is still eating, even though looking thinner than usual.
As for the area animal welfare people, I have never had good luck with ANY of the agencies. They either don't respond to messages or tell you they have too many cats and/or no time to help. This is very disappointing.
Thanks to everyone who's given me suggestions and encouragement. I'll keep you posted.