Why do you want to accelerate growth?? Isnt he growing enough normally? Check with your vet whether his weight is proper or not. If he is having appropriate weight then dont try to accelerate growth becuase if your pup grows very fast then later in life he may develop hip or elbow dysplasia or some other disorder of joints. Let him grow naturally.
Proper growth depends mostly on diet. What are you feeding him right now and how much? May be he is not getting a proper diet. Do you add supplements to his feed? If not then you can opt for vitamin & calcium supplements freely available with chemists. Also some liver tonics will help him digest his food properly & thus will improve his health.
Dogs also require proper amount of excercise for growth. Is he getting that?
By 6 months he should have almost reached his full size. You can always compare your pup with its parents specially his father to know whether he is growing enough or not.
Take special care to know whether he is getting a balanced diet with required amount of protein, vitamins, minerals, specially calcium. All these are most important for proper growth of his bones & muscles.
Apetizer & liver tonics will help him eat more & get more from his feed. Feed supplements will supply required nutrients. And a balance diet will take care of his basic requirements for growth.
Also you should consult your vet before chosing an apetizer & liver tonic.
Best of luck.