For TYFTC comments, I say: "Thanks for the support and you're welcome!"
As for other comments...
For this one, since I have no way to answer the feedback, I just gave him a react.
For this comment, I told the reader what I have in mind.
For this one, the reader gave a suggestion...
And while it is a good one, it's not 'in-line' with my work, so I answered him:
Any case, these samples above are 'kinder' than the ones I received in my earlier volumes. This one below, is for when the reader was in the crucial parts of the story...
As you can see, he was telling me his frustrations. So, I answered it with...
Our 'talk' eventually led to this...
So, point of the matter is, I'd really suggest you answer the comments/feedbacks of your readers as much as you can. Not only would this make your concepts clear to them (in case they missed a few lines in your story), it would also give you points in the 'interaction' part.