If they are hookworms, it might take something strong to kill them off, with multiple treatments. If they are round worms, a basic de-wormer should have done the trick, but some require more than one treatment.
Can you send the pictures to your vet, as he.she can tell what to use,
Take a sample of the poop and this worm to your veterinarian, who can help you identify the worm and treat your dog appropriately. He can suggest some deworming drugs for various kinds of intestinal worms. Because some puppies get these worms from their moms, it is advised to frequently check their stool.