I used to work on the Amex account at Ogilvy and during the 1980s Ogilvy and Amex invented many of the new rules of database and promotional marketing.
One of the perennial winning offers was called Member Get Member– if you introduced five new members you got a case of wine. Wine was always the winning offer ( rather than whisky which also we tried out) because you could share the spoils with the friends you had introduced to membership.
I see this basic idea come up all the time in different guises. This latest is from Uber- who have come up with a fresh spin on it
BTW- feel free to use my code and get a free taxi ride with Uber