Facebook's not a bad place to have a web presence (it's a good way to get your real life friends into your comics, especially) ... but you should never pay to advertise on Facebook because it's a bit of a scam. Here's why (without getting too complicated):
There are two main ways to advertise with Facebook, and both are bad.
1) Advertise to get more followers.
If you do this, then Facebook WILL get you many more followers, and quickly. However, no matter what areas and demographics you target, the VAST majority of the followers/fans that you'll get from Facebook are not real accounts. They are dummy accounts. Blackhat (or sleezy tactic) Marketing companies hire people to create dummy Facebook accounts and like pages en masse. Why they do this is a more complicated matter about the nuances of Blackhat Marketing and how it works, but it's a problem for your page. Here's why:
When you post on Facebook, the site's algorithm determines how many of your fans/followers/friends will see your post based on a ton of variables. The more likes and comments and shares your post gets, the more "reach" you get; the algorithm pushes your post to more people based on engagement. The problem with spending money to get more followers is that those followers WILL NOT engage your page. They won't like your posts, or comment, or share.
So it's better to have 100 followers who are more likely to engage with your posts and care about what you're posting about than 10,000 followers that are 99% fake. If you post to 10,000 followers and don't get likes/comments/etc, the 100 people that actually want to see your posts are not likely to ever see them. If you post to 100 followers that care, more of those people are going to engage, and you're more likely to get them to do things to promote your work (subscribing on Tapastic, giving to your Patreon, checking out your website, sharing posts with their friends, etc).
2) Advertise to get more "reach".
This is a little more of a psychological problem. Sure, you can pay Facebook to have your post seen by more of your followers/fans. You can even pay Facebook to have your post seen by your fans' Facebook friends that aren't following you. That sounds like a good thing, at first, but it's not:
It's a scam. The more people pay Facebook as a way to get their friends/fans to actually see their posts, the more Facebook continues to reduce the "reach" of non-paid posts to maximize their profit. By paying to advertise to people who already WANT to see your work and their friends (who are more likely to care about seeing you if your fans share your posts rather than a paid advertisement popping up in their feed), you're supporting a Facebook marketing system that is becoming more corporate and less user-friendly. And if you do advertise a post to non-followers, you'll start getting more of those fake followers that I mentioned above.
Facebook's a useful tool. Get more engagement/likes/followers/shares by writing posts that are calls to action, that give simple and clear instructions for how people that want to support you can do so, easily. Ask your fans questions, get them involved with your brand. That's the way to build an organic following that will actually help you grow. It's nice to have a bunch of fans, seeing a high # is nice, but it's MUCH better to have a smaller, more engaged fanbase ... especially when you're trying to grow.
It's sort of the same here on Tapastic, though to a lesser extent. My comic, Atonement, hasn't had a spotlight or a staff pick yet, its style is sort of experimental, and so I have a fairly low subscriber count compared to a lot of other comics. But my subscribers and I chat a lot, we're very engaged with each other, I have a great like/comment-to-subscriber ratio, and so I feel like each of my subscribers are super valuable to me. And because it's that sort of organic growth, I'm more engaged with them, too.
Not saying that getting a spotlight/staff pick is a bad thing. It's an awesome thing to have happen to your comic! I don't think that there are any creators here that wouldn't welcome that big boost to readership. But there is something particularly valuable about building a following from the ground up, too.
In short: use Facebook as much as it benefits you to do so, but I'd never pay for their marketing. Hope that helps!