You can't increase his/her genetic limit for growth.
You can, however, influence some tissue growth (bone density, muscle, fat etc) through diet and exercise thereby getting closer to that growth - but that is not advisable to consider until he/she is an adult.
If your dog is still a puppy, it's a terrible idea to overfeed, as that pushes your dog is a disasterous direction.
Don't forget that every tissue in a dogs body is made of different "materials", and has varying degrees of blood supply - this means that different tissues grow and recover at different rastes, different tissues heal at different rates. During growth spurts, different tissues grow at different times as well.
Overfeeding can exaggerate growth in some tissues, while slowing growth in others, thereby encouraing a disproportionate growth that can dramatically affect your dogs life in the short or long-term.
...and that's only considering how overfeeding affects tissue growth - that's not even mentioning the potential digestive, nervous, immune etc potential effects.
I know of sooo many runts that became HUGE and sooo many huge puppies that just never grew much into adulthood.
You might just want to feed your dog a healthy amount of healthy food etc and wait for him to grow on his timeline - not yours.
I realize "hope" isn't a great strategy for growth, but it sure is healthier than trying to force growth on him.
You're dog will only grow as big as his genetics will allow. Premium food, supplements, physical training to build muscle ect will only allow him to grow to his max potential, no more. You will never see a Pit develop into Bullmastiff size, unless the lines have been bred bigger, often with outcrosses. Genetics = size, color, muscle mass, athleticism.
Bigger doesn't mean better. You don't want your dog to grow too fast, as this can lead to health problems down the road, and as he ages. I read about a study on a number of Labrador litters, half were free fed throughout their lives, while the others were fed controlled portions. The free fed dogs tended to be fatter, and generally not as healthy as the controlled dogs. The average lifespan of the dogs was the same, but the decline in the senior years for the free fed dogs was markedly more advanced than the dogs fed a controlled portion diet. Over all the controlled diet dogs were more healthy, at every stage in life.
If you want your pit to be bigger to be more intimidating.... that's a whole other can of worms. I can't imagine any other reason anyone would want their pit anything other than what it was. Pits are very capable dogs, regardless what size package, whatever the task.