I have a profile on OKCupid. It gets "Liked" a lot. It's not that I think I'm all that and a bag of chips, but I didn't write the same boring, "I'm looking for a nice girl. I'm a really nice guy. I'm into anime and music. Blah, blah, blah" that every desperate dude puts in his profile. Instead, I tried to convey that I am an interesting and worthwhile guy by how I wrote my profile.
With that said, I find online dating extremely awkward, and I say that as an introvert. To me, it's like searching through products on Amazon. When you meet someone in person, you can generally gauge if you have chemistry right off the bat. Sure, there may be something about them that instantly attracts you to them, but it's not like you read through a profile and matched up the features you want in a mate. With online dating, you're testing the waters with someone that seems like you have something prima facie in common with, but it just ends up being awkward with trying to actually create chemistry with someone with whom you have absolutely no history. And writing messages or even talking on the phone is not the same as meeting someone the traditional, organic way.
I have gone on dates via online dating, but I've never had a relationship develop from it. While I have an online profile, I have never really taken it seriously. The hard truth is if you're a guy, the odds are stacked against you. Any mildly attractive or interesting female on a dating site is inundated with messages from all types of guys, from creepers to legitimately good dudes. If you want online dating to work for you, then you seriously have to stand out and be willing to play a numbers game.
This is just my experience as a guy in his early 30s on a free dating site. It shouldn't be taken as being indicative of everybody's experience or empirical research on dating site success.