Two social networks dominate the current social media market: Facebook and Twitter. Because of the sheer number of users across all demographics, it is essential for any out-of-app marketing campaign to make use of these, and, when possible, to do so in-app as well.

At its core, viral marketing is any method of acquiring users that provides more than one additional user for every new user acquired. There was a catchy Faberge Shampoo television commercial in the 1980s that featured Heather Locklear saying, “It was so good I told two friends about it. And they told two friends. And so on, and so on…” — all while the screen was dividing up into smaller and smaller squares with new faces. Viral marketing is like that.

The good thing is that viral marketing doesn't completely depend on just one channel any more. In fact, to maximize those areas that are overachieving and to tweak areas that need improvement, it's good to utilize as many channels as you have the time and resources for. If you can utilize all your channels, and the end result is that your overall cost per new user (all social marketing costs including YouTube videos, websites, support, Facebook fan pages, Twitter campaigns, and so on) is less than their expected lifetime value or expenditure, then your campaigns are paying off, regardless of the viral component. The terms cost per user acquisition (CPA), customer acquisition cost (CAC), and lifetime value per customer ...

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