I have a 4 week old puppy, mother will not nurse do I need to give it any kind of milk supplements

Yes, Petsmart sells 21st Century Milk Replacer Food Supplement for Puppies, but at four weeks this can be mixed with a good quality puppy chow, wet of course, after mixed. Your vet probably sells a puppy milk supplement as well.

What kind of dog is it, and how many pups were born?