Try this: go on Tapas and try to find your comic without typing the title into search. If you just updated, you might appear in Fresh for a few minutes before other updates push you off that page. Try searching generic keywords someone might use when looking for something new. Look at the first page of each of the genre sections. If your comic doesn't easily appear using any of those methods, at least half the problem is that you're so far removed from basic site traffic that people just aren't finding it at all.
So to combat this you can make sure your icon is as eye-catching as possible. You can add tags to increase searchability. And you can improve your comic so that every update encourages people to like. Even if your subs are low, you can get into trending if the ratio of views to likes/subs is high enough. So pay attention to which updates are getting the most likes, it might tell you what your audience is motivated to click for.
Of course there's also advertising off site, but that's a whole other topic and a lot of work in itself.
