Self-Promoting
That's pretty much it, until you reach the turning point and fans start to find you organically. I've had to promote my Tapastic series just as much/often as my official comic site. And since I'm offering something slightly unique and different with Tapastic being the only place my series is in vertical format infinite canvas, I'm able to push that along side my official site's update posts.
Also, these forum threads for more advice:
You can do both ads for your blog site and your Tapastic profile on PW (it's more work but possible). Lately, I've been just promoting my Tapastic profile on my many social media profiles and that's seemed to work just fine too.
Of course, there's also being active on the Tapastic site. Engaging with other comic series (without self-promotion as a motive), Thank you pics on the sub's wall, Fan art of your favorite comics series (the other artist might be nice enough to share on their social media), guest comics, so on. I like to call these methods indirect advertising because just your mere presence (without promoting being your intention) builds a reputation and possible curiosity for people to click on your username and check you out. For social media it just helps being everywhere. ;D