It’s harder to gain new customers than it is to retain current ones. Similarly, it costs more to develop new customers than is takes to maintain current ones. The trick in all of this is to put out something so original and appealing that the die-hard fans help you to bring new followers in to the fold.
I’ve talked before about making the customer believe you, but your goal is to build such a brand loyalty that the believers spread the message. Word of mouth about a product will provide a more lasting interest than any retweet, interactive ad or athlete sponsor ever could.