Viral marketing
This is a technical problem discussed in Social Media Analysis 10-802 in Spring 2010.
Viral marketing refers to marketing techniques that use pre-existing social networks to produce increases in brand awareness or to achieve other marketing objectives (such as product sales) through self-replicating viral processes, analogous to the spread of pathological and computer viruses. It can be word-of-mouth delivered or enhanced by the network effects of the Internet.
The goal of marketers interested in creating successful viral marketing programs is to identify individuals with high "Social Networking Potential" and create viral messages that appeal to this segment of the population and have a high probability of being taken by another competitor.