How this growth loop worked
A guest who had a good stay sends a friend a referral link carrying travel credit. The friend redeems it and books a first trip at a discount. A strong first stay turns that friend into an active traveler who sends their own links, or lists a spare room as a host. Every satisfied booker becomes the next sender, closing the loop.
Airbnb rebuilt the referral to hand the credit to the friend, not the sender. Framed as a gift rather than a payout, it read as generosity, and conversion climbed. A referral K well below 1 never sustains itself; the loop amplifies, it doesn't run on its own. Its real work was lowering blended acquisition cost, since every paid or organic signup pulled in a fraction of a free one.
Design the incentive around the receiver, not the sender's payout. A credit the friend spends on a real trip removes the awkwardness of a pitch and gives them a reason to book now. Attach the loop to a product people already love, so it fires only after an experience worth passing on. Then judge it as a cost multiplier on your other channels, not free, self-running growth.