Surprisingly, yes you can breastfeed your puppy. This is something that has been practiced in some cultures for centuries and is still done today in some places.
However, it does carry some risks. If you are lactating I assume that you are also feeding your own baby. If that is the case, there are zoonotic diseases that can be passed from the puppy to the baby via your breast.
Also, it is not a huge concern to breastfeed a puppy in an emergency, but human milk does not have all the nutrients a dog will need.
Feeding him human milk could stunt his growth and generally damage his health. He needs to get onto a canine feed as soon as possible.
If the puppy is tiny, he will also need to bond with his mother in order to learn from her all the instincts that dogs need to keep them safe and make them independent.