Its not bad. And very specific

The specificity of your app makes it that much easier to "reach out" to your demographic.

You need to be on the social networks as much as possible.

for example http://www.reddit.com/r/comicbooks

Also go to those cos play conventions and advertise on the floor. Get a stall

Maybe you already thought of all this but the biggest thing to remember is that it will take time because of how specific your app is.

If you want more and more people to use the app start selling action figures/ toys/ other comic book relevant stuff

I don't know anything about that stuff good luck