You should really get to the root of his hair loss. This is not a usually occurrence and is mildly alarming. Is this a nutrition problem or a food allergy? Has he been on any meds lately? Has their been a stressful change in environment? Finding the source is key.
DO BRUSH YOUR DOG DAILY in the direction of hair. Give him a good and nutritious food for his better health. You can consult veterinarian for his food advice. don't ever le give him human food because it is nutritionally unbalanced and does not provide necessary minerals and vitamins required for his healthy growth. human food contains fats which causes hair fall in dogs.
You should definitely take your dog to the vet, if you haven't already. A common cause of hair loss is allergies, but it can also be a sign of serious diseases. You will need a vet's help to identify the cause of the hair loss.
At first you may consult a vet doctor and have a check up throughly, then according to his advice you can use the medicines prescribed. Give bath with good soap and apply medicated oil which suits its health. By giving drugs also the dog can retain its lost hair slowly.