This sounds like something where, if people don't respond strongly, make the choice you want to make.
If you tell your current audience, "hey, I'm thinking I'd really like to finish this comic up and work on a new comic, but I do enjoy this making this one, and I could stick with it if enough people really want it to continue -- what do you guys think?" and you don't get enough people telling you that they really want you to stick with it because you simply don't get many responses......... then don't worry about it, go ahead and start on something new! You're free to do what you want to do.
I really feel like getting a responsive audience is something you can't force. There's no way to demand other people put themselves on the spot or force them to be open with you -- you can only put yourself out there, and hope some folks respond in kind. The way you interact, the way you talk in the page description or in replies or on social media, the kinds of things you draw outside of your comic -- that's all you've got.
The weird thing is, though, that it kinda is a numbers game. Only a tiny portion of any audience is gonna be outgoing enough leave comments. It's gonna be REALLY HARD to have 70 subs, and get 10 of them leave a comment or respond to a question, just because of how small a percentage of readers are vocal. So, how do you get at least 10 folks to respond to a question? Have at least 200 subs.