I guess this could be because I "grew up with" a more demanding sharing culture online that required more active promotion (such as deviantART and various discussion forums I was on), but I didn't really ever expect a site to take care of promotion for me. It will do that once you have built up a larger following and update regularily, but until then you need to do active promotion through social means, sharing and perhaps even project wonderful.
It all depends on what you expect to make of your comic and how much you're willing to invest. The results will reflect that. If you're not planning to do comics professionally, I wouldn't bother honestly because active promotion is only fun if you're a business nerd that enjoys the action of promotion and studying how various techniques and actions affect the flow of the numbers. If that's not your thing, I suggest you just sit back and do your comic because you like to (: How many people you've got reading it or not doesn't matter if the main reason you draw is because you love it anyway.
Upload on multiple sites! Webtoons or smackjeeves are the most common alternatives besides Tapas, but aside from that you could also try tumblr and deviantART! Different comics find different levels on success through different means (: I know in my case, for example, smackjeeves isn't very effective at all. Tapas, however, has always been effective for me. Even on my less popular types of series (for example I have a horror series). Other people experience the very opposite.