Social media (SM) has become an essential means of engaging key stakeholders for business-to-business (B2B) firms. As a result, academic research has paid increasing attention to the factors that drive SM engagement in business markets. Although studies have examined the types of SM content that generate higher engagement in B2B contexts, current research lacks deeper insight into message strategies across different social media platforms (SMPs). We address this knowledge gap by examining whether the use of SM content strategies by B2B firms varies across platforms and whether their effectiveness in generating engagement varies across SMPs. In doing so, we build a new SM content strategy framework focused on messaging functions that capture a broad set of message stakeholders. Using advanced Random Forest modeling, we analyze 1700 SM messages and related engagement data from 18 of the largest Canadian B2B companies based on their revenues. We advance current research knowledge by demonstrating how different message strategies across SMPs achieve higher engagement levels. The findings offer concrete insights for practitioners to effectively engage diverse stakeholders across different SMPs.