Labrador of 17 weeks is skinny and has little or no appitite

Question
My Puppy was the runt of the litter and on the skinny side when i bought him from the breeder at 12 weeks old.  We decided to take him on and feed him up as he has a lovely nature and is very quite.  The problem being he will not eat any dry food so we changed him to a wet diet of meat and now he eats a little. Is there something i can give him to beef him up a bit.  Someone at puppy playgroup with a very tubby pup mention puppy milk.

Answer
Hello al dogs wil eat dry food if its left down for them, get a highquility pupyibble for large reed puppies and canned food of the same you can mix them together slowly reducing the canned until he is eatting only the dry, Ppuppy milk is for puppies that there mother wont nurse its not advised to give to older dogs.  Its also possible since you say he has little appitate...labs are alway hungry and is veryskinny hemight just have worms...see his vet for a deworming.