NPS Follow-Up Question

We just launched our first NPS program and are having some internal debates about how many times we should follow-up with those that don't initially response. Additionally, how many outreaches should we do to those who did respond and we want to gather more information from. 

I feel like there should be no more than two outreaches in either situation - anymore and you run the risk of annoying your customer. But, I would love to hear varying opinions and the 'why' behind them. 

Thanks!