It can be tough to raise a pup on just raw. But you should be able to get a little more weight on him, you don't want him fat but you don't really want his ribs showing either. Pups grow a huge amount very quickly so you want to keep that in mind.

Are you feeding him once a day? Pups should eat more than once a day. I would feed him twice a day or maybe even 3 times if you think he needs it.

Certainly up his food and add more fat, such as full fat cottage cheese, maybe even make up some Satin Balls and give him those too. (You can find Satin Balls recipe on line, it is a common thing to add weight to a dog or pup.)

Is he getting raw bone with the chicken? They really need the raw bone in the raw feed. Adding more chicken such as backs and necks should help too. I don't feed organ meats every day, just a few times a week. Coconut oil is good too, and so is the salmon oil you are giving.

Maybe even add some high quality kibble for one meal, that might help. I would rather add a good kibble than rice or other filler as at least the kibble has meat meals and vitamins in it.

Some pups just grow slower but you should be able to get a bit more meat on his bones so his ribs don't show. Is he getting exercise and time outside in the sunlight? That is good for growth and health.