Social networking sites (SNSs) are quickly becoming the main venues for social interaction of Internet users. As the competition between these online services is growing ever stronger, the success of SNSs derives from persuasive core application designs that influence users in taking specific actions, such as joining the community or recruiting new users. Therefore there is a need to identify relevant, value-adding features that facilitate social interaction and that are integrated in the group’s socialization rituals. The present study employed Cialdini’s framework in the analysis of SNSs design characteristics that facilitate social influence leading to the fulfillment of site marketing objectives, such as member acquisition, member retention and user loyalty. We examined social application features of the three major Romanian SNSs, i.e. Facebook, Hi5 and Neogen on six dimensions corresponding to Cialdini’s social influence principles: reciprocation, consistency, social proof, liking, authority and scarcity. We thereby extract core application commonalities and differences and identify design gaps from a social influence perspective that are to be explored and exploited as a source of competitive advantage. Marketing implications of the results are discussed