While recent research has increasingly indicated social media brand communities can bring about desired benefits for firms, the trade press has cautioned the unsustainable growth issue of such communities. Given that the realization of their benefits is contingent on sustained growth, this study investigates the role of two types of content central to sustaining these communities i.e., marketer-generated content (MGC) and user-generated content (UGC). Furthermore, we delineate between content of product-related (for product promotion) and social-related (for relationship building) nature. Our findings show that both social- and product-related UGC can promote growth over time; but only social-related MGC is effective in this regard. However, MGC regardless of their nature may stimulate UGC. Overall our findings suggest that sustaining the growth of a brand community requires a symphony of both marketer effort and consumer response, thus providing a more comprehensive and balanced view of their role.