Building a readership takes time and patience. You'll get die-hard fans that stick by you for years... and you'll have those who come and go over time. It's juts the way of the Internet.
Though I've hosted my own comic on a self-made site for many years, I came here because I wanted to branch out and meet new people, and comic creators, to share with. I'd agree that taking interest in other people's works will increase your own exposure -- I'm very likely to click through a comment on my comic and read/subscribe to that person's work.
Posting on forums and staying involved in conversation also helps, especially if you've linked your comic in your forum's profile (which you have).
Overall, don't give up your art, even when you don't feel like people are reading. Keep in mind that there are slump times even for the Internet. In my experience, less people comment in the summer months and around winter holidays, simply because they're busy. So expect a slump time and you won't be too disappointed. Once school starts, things pick up again (I guess kids are slacking on the Internet at school?) 
You can never tell who's looking at your stuff and who you've made smile for the day. Not everyone who loves your work will comment. Draw comics because you love art and your stories, and the rest will follow.
