This is a whole new category of study for me. Here are few sources that are getting me started.

Keith Schacht writes an amazing detailed how-to for analyzing your product’s customers entitled Web and Mobile Products: Understanding your customers, while defines the term viral loop and how to build your own viral loop in his article What’s your viral loop? Understanding the engine of adoption.

“Regardless of a company’s earlier success, thriving in the new mobile app economy depends on engagement and retention. After acquiring users, the real battle to keep and ultimately monetize consumers begins”, from App Engagement: The Matrix Reloaded.

“the power of the network effect is fading, at least in its current incarnation. Traditionally defined as a system where each new user on the network increases the value of the service for all others, a network effect often creates a winner-takes-all dynamic, ordaining one dominant company above the rest ..” from The Network Effect Isn’t Good Enough.

“A viral product derives much of its growth from its current users recruiting new users. A user could recruit another through a simple invitation (“Check out this product, it’s cool/useful/entertaining!”), or directly through using the product (“I want to send you money on PayPal!”)”, from How to Model Viral Growth: The Hybrid Model.