I've used online dating sites, and found them quite effective. My girlfriend of over 2 years and I met on an online site. A close friend of mine met his wife on an online site. So, they do actually work.
I remember when I gave that idea a go and found I generally sent out tons of emails but rarely got any responses.
This probably means your emails sucked. Did you send a one-sentence email? Something like: "I saw your profile and you seemed interesting so I thought I would say hi." Where was your effort? If you want to meet someone, you need to demonstrate you are interested. Did you point out your similarities, common interests or things you both enjoy? You need to show that you aren't just some random guy spamming a hundred girls to see what will work. Does she have a cat or a dog? Even if you don't have one, you can mention that you used to, or you've wanted one, or ask how much the darn thing sheds. Just something showing it's personalized and, most importantly that you read her profile.
While I have met people online, I've definitely found my chances are significantly higher in person, face to face.
Again, that's probably because your emails sucked. There is no tone of voice, no body language or dimension to an email, so you have to do it all with words. This isn't easy, and a lot of people suck at it because they've never had any practice. However, most people (although not all) have a lot of practice interacting with people in real life - even if it is just to order something from Starbucks - making them better at communicating in real life than in an email.
If I were to become single again, I would be back online right away. It's a fast way to find people who are interested in similar things, and to meet a lot of people that you wouldn't in your regular routine. (When was the last time you went to a coffee shop on the other side of town just to see if you could meet someone new?)