As a new author to this fandom, I would definitely tell you to keep writing when you enjoy someone's work. Feedback feeds the muse, and it is kind of you to let someone know that you enjoy what they are doing (whether they respond or not).
I would suspect that many of the authors who have not responded aren't fully aware of the etiquette. When I first started my fanfic career (in another fandom), I had some kind veterans give me pointers as to how to respond to feedback and build an audience. Otherwise, it would have taken me awhile to learn the ropes.
