This paper studies a novel social media venture and seeks to understand the effectiveness of marketing strategies in social media platforms by evaluating their impact on participating brands and organizations. We use a real-world data set and employ a promising research approach combining econometric with predictive modeling techniques in a causal estimation framework that allows for more accurate counterfactuals. Based on the results of the presented analysis and focusing on the long-term business value of marketing strategies in social media, we find that promotional events leveraging implicit or explicit advocacy in social media platforms result in significant abnormal returns for the participating brand, in terms of expanding the social media fan base of the firm. The effect is also economically significant as it corresponds to an increase of several thousand additional new followers per day for an average size brand. We also precisely quantify the impact of various promotion characteristics and demonstrate what types of promotions are more effective and for which brands, while suggesting specific tactical strategies. For instance, despite the competition for consumers' attention, brands and marketers should broadcast marketing messages on social networks during the time of peak usage in order to maximize their returns. Overall, we provide actionable insights with major implications for firms and social media platforms and contribute to the related literature as we discover new rich findings enabled by the employed causal estimation framework.