Satin Balls are for addressing transient weight issues for sick or stressed dogs. They will not make a lanky adolescent dog mature and filled out and buff... they will make a lanky adolescent dog pudgy. What you want is going to be result of genetics and maturation and physical conditioning.
I am not a big fan of Satin Balls. I do not feed cereals or sugars to my dog, or inappropriate fats. If I had an underweight dog, I would try to find a more nutrient dense and higher calorie food that was appropriate for dogs. I feed raw, so if I had a dog that was difficult to keep weight on, I would feed fattier meats and pass out the occasional extra egg.
use anyone to get him to gain weight
i would talk to a vet and see if he is at the correct weight (and to see if he healthy) before you start doing that stuff
I wouldn't suggest trying any strenuous physical activity yet, because at 1 year, I doubt your dog is fully grown. This can lead to adverse effects on the joints. If you can feel your dogs ribs, but you can't see them, he should be fine. If he's not fully grown, he obviously won't be at adult weight yet. He sounds like he's getting close. If you're really worried about his weight, I suggest talking to your vet.