Here's what I do to engage interaction:
-Not really something you can plan in the middle of your story, but make sure your story's world is expansive. There needs to be something to talk about: Be it how powerful the characters are, the power system, the political system, character's feelings and opinions of each other, etc- And multiple of these at a time, but not so much that your reader gets overwhelmed.
-Always have an unanswered question. These can be big, story-developing points, or small multi-chapter mysteries. Of course actually answer the question in a satisfying way eventually or the audience will grow to distrust you, but that's another whole course on writing and stuff entirely. People will pour their theories into the comments.
-Some people think it's kind of cheap, but it's something I personally find unavoidable in my own story (and many others) due to the nature of how long it takes to resolve conflict, but, ending on a cliffhanger will compel readers to leave comments with predictions on what the next episode will be like.
-Have really strong, emotional moments. If the reader is overloaded with emotion, they'll need SOMEWHERE to pour it out, and that place is the comments section. Things like: A kiss, a kill, someone crying, etc.... Just things that trigger the reader to spam emojis out of shock/sadness/excitement/etc.
-I always end my chapters with a Q&A (one question) and a lot of people will post questions for next week/their response to my question this week in the comments section.
-I'll also end some chapters with a unique illustration, and people will leave their comments for that illustration in the comments section as well.
Hope this helps!