An organizing framework for viral marketing that highlights different behavioral mechanisms underlying knowledge-sharing influence and compliance in online social networks is proposed. The two factors that influence viral marketing include role of the influencer and network externalities. The role of the influencer is to create awareness and signal benefits to others within their social network and can be influential in encouraging trial and adoption of new products and services. The information provided by influencers enable the site to successfully serve a broad audience in a focused manner. Motivated evangelism (ME) comprises contexts where recommenders play and active role in influencing connected users and there are significant network externalities accuring to influencers and recipients.