I'd also give him a little Kaopectate or Immodium.
KAOPECTATE/IMMODIUM (loperamide):
Can be given to dogs and cats (1 teaspoon for every 20 pounds) for diarrhea. This dosage can be repeated every 4-6 hours for 24 hours, or until symptoms begin to resolve. OTC Medications
Remember, toy breed dogs can dehydrate really quickly from diarrhea. If he doesn't improve within 24 hours, you need to take him to your vet.