Have you noticed the new button "Bring Your Friends" just take a quick look at the page position top right. Actually this is Facebook invite friends API system. For implementing this you have to create a Facebook application to setup your webpage canvas URL, just few lines of code but before that your web page should be SSL (https) enable.
![Facebook Invite Friends API](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwuK2axpBKek0kvANbLPS46kGV2WizF8jVT38ZIWeo1BWqfjKwr-YF8R8sRDCaFTwADqTLkLhqPvgi_7e3VJ61oXoCq35QVPltA6G-mUF3hkzz0njn9xZ6K7oEMNZsmBJ79wpb90X6Xzhk/s550/fbfriends.png)