Abstract: Social media are increasingly popular. Consequently, marketers more and more recognize social network sites as a platform for commercial campaigns. Social network users forward these campaigns to their online connections. However, our understanding of the persuasiveness of these campaigns is scarce. This study takes on the perspective that social context plays an important role in explaining campaign effects, and investigates whether the social connection between the sender and the receiver of a viral social media campaign predicts its persuasiveness. More specifically, it is tested whether strength of tie between the sender and receiver of a campaign predicts receivers’ affective and behavioural responses, and whether perceived persuasive intent is the underlying mechanism. The results of a survey among social media users obtained support for this idea. Thereby, this study contributes to our understanding of viral marketing communications in social network sites. Implications for the prospect of marketing activities in social media are discussed.