Drupal pay with tweet / social media
In case you are wondering if it is possible to show only a snippet of a block of text/content and allow people to see the complete content or enable a download only after they have shared it on social media - like twitter, facebook, google plus, etc, in drupal , then some of your problem will be solved with a contributed module.
There is a module Pay with a tweet, Pay with a tweet implements tweet payment feature. This allows the website to make downloads available to users with a tweet as payment. Pay with a tweet provides a token and unlimited blocks to show the downloads.
Your visitors will get content without having to pay money and the website benefit from this viral marketing system based on the social network Twitter. You can checkout this website for running a campagin http://www.paywithatweet.com/ , http://www.estago.com/
Similarly there is work going on where you can also pay using Facebook Post. Check this node for details