How old is he?
How much does he weigh?
What brand of food are you feeding him?
Look at the back of the bag, what are the first 4 ingredients listed?
If the first 4 ingredients in the food contain any of the following: corn gluten meal, meat by-product, wheat gluten, rice gluten, then the first thing you need to do is find a better food.
Here is a website to help with that
Has your puppy been dewormed? If he hasn't then he mostly has intestinal worms that are taking all the nutrients away from his body, so you should take him to the vet and deworm him.
Adding canned food meals everyday is a great idea, same rules apply ingredient wise for canned foods too.
Don't mix dry and wet, just feed him straight wet 2-3 times per day and always have dry out for him to munch on.
Is he drinking water? I worry about him not eating and get hypoglycemic (sugar disorder) add some chicken broth to his water if he is not drinking alot, and you can also pour it over his kibble.
If he does not improve using these methods within a day or two, take him to a emergency vet.