Learn how to use the Audience module to find which entrants have referred/shared your promotion the most
First, go ahead and open the Audience module.
You should now see something similar to this.
You should see Referrals (Entry) in the headings. (If you don't hit the drop-down with the three lines icon next to Export and tick it in the menu that appears)
If users have entered as a result of clicking on a link shared by a previous entrant, then they will be shown in the list here. (click the Referrals (entry) to re-order, so it shows those that referred the most at the top).
In the example below, the number 13 is the number of people referred by this person. Clicking on this number would then reveal a list of all those people that entered via their unique referral link. You can also use export to view this data in a spreadsheet.