Depends on the reason the dog isn't eating. I'd rule out any medical conditions first. Have you discussed with the vet.
Some dogs are picky eaters and some dogs may have medical problems. Before suggesting anything I suggest you consult your vet.
A dog so small should not go w/o food/water for days it can dehydrate and die!
Cats only have nine lives because they stole them from dogs!Teehee