Abstarct: Online marketing communications are moving toward interactions between individual recipients and consumers rather than being directed from a marketing organization to masses of consumers. As more and more marketers attempt to harness the power of electronic word-of-mouth (eWOM) in social networking sites, rigorous investigation of determinants that lead to consumers’ engagement in eWOM via the social networks is becoming critical. Considering pervious studies that have recognized determinants of eWOM, knowledge sharing and email receivers pass along behavior, a frxamework of the most effective factors have been developed. Using two samples consisting of Iranian adults and not Iranian adults, this study investigates relationship between four Social Relationships variables (social capital, homophily, trust, and consumer susceptibility to interpersonal influence), and four individual variables (openness to experience, extrovertedness, self-efficacy, consciousness) and eWOM behavior in social networking sites. Results from a series of multiple regression analyses indicate that in Iranian and not Iranian societies Bridging Social Capital, Trust, Extrovertedness and Self-efficacy are significant predictors of opinion leading. On the other hand, in Iranian society there is a negative relationship between Bonding Social Capital and Opinion Leading. In addition, Bridging Social Capital, susceptibility to interpersonal influence and Self-efficacy are influential over Opinion Seeking behaviors