The Facebook Tool
Tools >> Facebook Referrals
The Facebook tool will display a list of people who shared their registration on their Facebook page and a count of how many times that link was clicked (Referred) and the number of times that referral lead to another registration (Registered). You can use this information to incentivize people to spread the word, have contests, etc. The possibilities are limited to your imagination.
Participants can share to Facebook via their receipt or their registration history.