As of March of this year, Airbnb is valued somewhere around $20 to $25 billion. That’s nearly double what it was worth this time last year -- impressive for a company that didn’t even exist a decade ago. But more impressive is how they achieved such staggering growth in the matter of a few years. The answer is simple: referrals. Airbnb took a straightforward referral approach by sending email invitations to existing participants. The offer was enticing: referrers would receive a $25 travel credit when new members took their first trip. Then, they would receive an additional $75 credit when they hosted a guest for the first time. From Airbnb’s perspective, the referral program was a no-brainer. After all, they were only paying for referrals after new users made a purchase. This ensured that they weren’t wasting any money on unprofitable referrals. The program worked (and still does), helping Airbnb to achieve incredible growth, in which the total number of users has practically doubled each year since 2012. Get the full story at Entrepreneur Read also "This chrome plugin supercharges Airbnb for sightseeing" at The Next Web