I am not to sure about pit bulls, but my sharpie had a similar problem and I had to take her to the vet. She had the allergies and lacking vitamins. I had to give her benadryl and mix this powdered mixture in cottage cheese.

Please take the animal to the vet it can also be the mange.

 If there is red scabby rings then this is most likely ringworm. It can cause hair loss around the spots. It is a fungus and it's highly contagious even to people so wash your hands thoroughly after touching him. Hair coming out in clumps can also be a sign of mange....either way you need to get him to a vet so they can do tests. Check your body for any red spots like his, if you have any then this is ringworm and it will take a little while to clear it up but athlete's foot cream will take care of it. But don't use that on the dog, a vet will give him a cream, drops, or a shampoo to clear it up.