Hi and welcome to Just Answer!
Is your dog on a flea/tick preventative and if so, what brand?
Not at this time he is not
Are the spots red? Is there any exudate from the skin that might indicate infection? Have you looked carefully for fleas?
The spots are not red. It looked like dry scab when I looked at it closely, I haven't checked for fleas recently but have never had a problem with them.
The first thing to rule out is external parasites such as fleas. I would recommend a name brand preventative such as Frontline or Comfortis. Alternatively, dogs can have allergies that lead to hair loss and potentially a secondary skin infection. Only an exam by your local vet can confirm this and if present antibiotics and an anti-inflammatory such as prednisone can be prescribed as treatment.
For something to try at home, a medicated shampoo with colloidal oatmeal would be a good option in addition to benedryl (diphenhydramine)... about 25mg orally twice daily. I believe that Frontline can now be purchased at Wal Mart.