I might as well throw this pessimism reply in early, so it can be overshadowed by better stuff. If you like, take it as a host of things that MIGHT work if you're NOT ME? Because all I have is the web too, once you discount my beta reader and my wife.
I'll start by agreeing with Wildbow's remarks above, yet noting that (from my experience) consistency and frequency aren't enough... online promoting needs to be a thing, somehow. Starting out, for 66 weeks, I published 118 updates, and (in the end) had only 10 views on them. Alternatively, my current effort has been running nonstop for 28 weeks and I'm getting about 5 views each post. (I won't comment on my writing quality... but I used to win convention fanfiction awards when I was in University, surely it can't be THAT bad...) The additional bad news is that in BOTH those cases, I was/am self illustrating the stories, and it obviously has made no difference. (Or if it has, that's... kind of sad.)
Despite that, I'll now agree with Khronosabre that illustrations would be beneficial in general. It's partly what interested me in Nina's "Fooled", and images draw the eye if you post on Facebook, Twitter, or other social media (as I do) more than mere text. Plus my new webcomic is getting 20 times the hits as my serial, and my drawing is MUCH worse than my writing, so I'm guessing it's the visual medium - or maybe the brevity. Point being, images will all probably will work better in your case, you draw professionally.
Speaking of social media, a Facebook page probably can't hurt? (My four-year-old project is up to 26 likes, my current one has 6 likes.) Meanwhile Twitter tends to be where I get an offhand remark (in 140 characters, rather than anyone commenting on the posts themselves), and I can schedule the update Tweet through Wordpress. You will want to send out more than one notification there, probably four or five, though I start feeling bad after two. Hashtags are your friends. (For anyone who saw the latest Doctor Who with the "Bootstrap Paradox", the Doctor acted pretty much exactly like my main character. I tagged #DoctorWho with a link to part of my story. One person looked, they didn't stay, but no one ever stays, so I'm still calling it a win.) Other people here have talked about Reddit, but I haven't tried that. Tumblr doesn't seem to be doing anything for me, but it's only been a month.
You might consider commentary asides, or guest posts from other writers... for whatever reason, my online friends will read THOSE, because non-fiction, but not my actual FICTION that follows; maybe you'll have more luck? Guest elsewhere, if you can - I had a huge spike with my "April Fool" update for "Legion of Nothing", even though no one's stuck around as far as I can tell. Also, commenting on other serials might help; there's another time travel one I monitor (I don't think the author's on this site) and after some remarks back and forth for a month or two, that author mentioned me in his online newsletter. (Again, seems to have gone nowhere for me.)
With "Epsilon Project", I had reader votes on plots every week, which is probably not where you're going (sounds like you have your Book 2 mostly written) but if you reworked it towards reader preferred illustrations or something, it might be another way to engage people online (even though it - you guessed it - failed for me). Hell, I suspect about the only thing I HAVEN'T done at this stage is actually sink money into social media advertising (because seriously, at this point, what's my motivation), but if you want information on marketing, Patrick Rochefort has put together a set of posts (search "Marketing Stats"). Oh, and I'd recommend putting a story link into your footer on the forum here. Occasionally, I get a random hit from WFG after I say something here in the forums.
In the end, I think some of it is luck, and some of it is genre. (Everyone used to like vampires, now it's superheroes. Romance is huge on Wattpad, time travel, not so much. Or, y'know, it's probably just me!) The rest is... Gods, whatever I'm doing, don't do that? Or do it much better. Then let me know.