Honestly AFF is bad with this and I'm sure a lot of writers would agree with me. 

When you ONLY comment, "moar pls" or "lol i want a sequel!" or "thanks author-nim" it's a bit annoying.

Don't get me wrong, writers love comments on their stories, but they like feedback. They don't want to be told to write more because we aren't your writing slaves. We write on our own time so just being told to write more is a bit offensive. And wanting sequels to stories is completely okay, but it's just how you deliver the comment.

When you don't say ANYTHING about the story you just read, it gets a bit tedious for writers. When you don't say, "Oh, I really liked when ___" or, "Wow I wasn't expecting that!" and just feedback that relates to the story, the writers have nothing to go on.

Just saying, "I want more!" gives us nothing.

Give us feedback. Tell us why you like the story. Telling us to "write more" or "Give us a sequel!" is basically like a slap in the face because it doesn't feel like you enjoyed what you just read, all you're concerned about is wanting more.

Without feedback, a lot of your favorite authors will eventually stop writing. 

Learn commenting etiquette and give writers feedback. They'll lose steam if you don't appreciate their hard work and just demand for more.

You are free to disagree with me however you'd like, but I think a lot of writers will relate to me when I say this.