Do you have another dog? Competition is a great thing to get dogs to eat.
I had a finicky eater (3 yorkies ago) and I would have to put the food on the FLOOR and not in a bowl. Weird, eh? We have to all admit they are little "bottom-feeders!"
Other things - they have to love what they eat. I know it's difficult but try changing his food tosomething different but very healthy and nutritionally sound. If you want some ideas, just let me know!