Make Your Site Go Viral With Viral Lock
The premise is simple. You simply protect your content with the [viral-lock] shortcode to stop it from being shown to visitors. Once the plugin has been installed, a lock icon will be added to your post editor to let you easily add the [viral-lock] shortcode to your post or page.
Once you have done this, your content will be restricted to visitors. they will instead see a box that asks them to share or tweet your page in order to see your premium content.
Viral Lock is a relatively simple plugin but it works well. It could be used to restrict premium content on your site or to hide download links for digital products you have released for free. I recommend checking it out if you are looking for a way to restrict content to visitors until they share your page.
A license for Viral Lock retails for $16 from CodeCanyon.
Link: Viral Lock