Hey there!, personally, i got an active and engaged readership. Here are some tricks i do:
Before being able to do events like a Q&A session, you need readers to be active.....
There are many techniques that may increase the posibilities of that....
1-Content: the updates of my comics was deliberately designed to give something to talk about, either by a joke, an important revelation, hidden details an eagle-eyed viewer could build theories around, or anything that evoke an emotion different than boredom. Pacing is key.
2-Games: sometimes i've made some activities like asking the readers to find a hidden character within the different pages. This naturally led to some posting answers....
3-Trivia: sometimes sharing fun/interesting facts about the creation proccess or characters can get readers to ask questions or start a conversation. Make sure you do that between chapters to not interrupt the flow of your story.
4-Q&A: this may require a readership that is big enouugh. If you get few questions at first don't feel down, answer them so wievers realize they can ask questions.......also, make sure you give a reasonable deadline. Not every reader will see your comic the same day is updated.