You're lucky, because coincidentally, I'm an expert on this.
Most shampoos that promise hair growth are a waste of money.
Scalp stimulation is indeed helpful, which I found surprising. On a trip to Sri Lanka someone told me an old ayuverda secret: massage your scalp with a lotion of some very rich oil (coconut, olive, sheabutter) and freshly ground black pepper. I did that and it was super effective. It makes you're scalp tingle very pleasantly. If possible, leave it in over night. But make sure you don't ruin your sheets.
Another thing that's effective are food supplements. Take lots of zinc and panthenol for about four weeks, you'll see the results quickly. be careful with the zinc though, one shouldn't take too much of that over a longer period of time.
I did both things combined and people actually asked me if I had gotten extensions, because my hair started growing like crazy all of a sudden.