You delight your customers who, when canvassed, are willing to add reviews. They share and recommend you to their friends and business connections because it is easy to do and the rewards, to them and to their friends, are desired as they are relevant.
Note that social sharing reviews promotes reputation awareness and that Refer-A-Friend and Other campaign sharing promotes referral campaign awareness.
Referral campaigns are designed to introduce new customers who may receive a sign-up reward and the referring friend may also be rewarded.
Your referral campaign is good to go. Now it needs to be promoted.