Discourse plays a central role in organizing vision and computerization movement perspectives on IT innovation diffusion. While we know that different actors within a community contribute to the discourse, we know relatively little about the roles different actors play in diffusing different types of IT innovations. Our study investigates vendor versus adopter roles in social media and big data diffusion. We conceptualize the difference between the two IT innovations in terms of their decentralizability, i.e., extent to which decision rights pertinent to adoption of an organizational innovation can be decentralized. Based on this concept, we hypothesized: (1) adopters would contribute more to discourse about the more decentralizable social media and influence its diffusion more than would vendors; (2) vendors would contribute more to discourse about the less decentralizable big data and influence its diffusion more than would adopters. Empirical evidence largely supported these hypotheses.