The explosion of free social sites and dating apps have allowed many single guys and girls to enjoy free communication. Google, Facebook, Twitter, Instagram all 100% free so we expect everything to be free and when it's not there is a surprise aspect like we expected everything online to be free of charge.
Tinder and Badoo are great examples of free social apps that help you find that special person however lately they have been experimenting with paid alternatives and limiting the amount of users you can see daily.
What one should understand about such services that appear to be free is that they are either run by ads that are very well disguised or they are being funded by private investment and are in the process of gaining users. When the site gains it's target active audience number it sells and the investor either repeats the cycle of increasing the user base or integrates some kind of revenue model on the existing user base.
The hookup dating culture that has exploded recently uses the same method of initial investment and later in the cycle of the products maturity you will see revenue generating models being implemented. For example the app Whisper allows you to anonymously share your secrets to the world and chat with anyone that has installed that app. They seem to be in the process of gaining a large audience and the popularity of the app is exploding.
Free social sites are the dating sites of the future and are already proving so with the multitudes of great apps available however expect there to be some ad models or pay to view systems in place in future. As competition increases those who are able to invest more heavily in technology win and that is usually those who strike the perfect balance between a great free service and a non intrusive ad system such as the popular facebook suggested products.