oh wow.
A tiny puppy can't go without food - there may be more going on then just the no teeth issue and you really need to go back to the vet and have him tested for parasites - If he is acting lethargic etc it could be coccidia or something worse - so as soon as you can - get him in.....
For now you may want to try a syringe for water & try what others posted but at that size and age you could lose him
If the breeder won't take him back for a bit then it's up to you to save him or give him to someone who will. I really don't understand why someone would want such a tiny tiny yorkie but that's a different topic and I don't want you to feel bad.
That breeder should be reported - some states have laws against selling puppies so young. What is wrong with people that they'd do this just to make a fast buck
Also - I would post where you got this tiny YOUNG puppy in the Breeder Review section so others know to stay clear. That is one bad bad breeder.