Social media message strategy is critical in determining how customers will engage with B2B firms on social media platforms. The present study examined the role of message source (i.e., firm-generated vs. employee-generated) and message content (i.e., emojis and objective information) in determining social media engagement. Four experiments were conducted to test the proposed relationships. The study findings revealed that employee-generated content leads to higher social media engagement (i.e., intentions and behaviors) than firm-generated content. Content-based trust and engagement-based trust were found to be the underlying mechanisms by which message source impacts social media engagement. Furthermore, we observed that, for an employee-generated message, including emojis has a greater impact on customer engagement than when they are included in a firm-generated message. Finally, no evidence was found concerning the effectiveness of incorporating objective information in social media messages on customer engagement. These findings have marked implications for B2B marketers in developing effective social media message strategies. •Message source influences social media engagement.•Employee-generated content results in higher social media engagement than firm-generated content.•Trust is the underlying mechanism by which message source influences social media engagement.•Emojis accentuate the effect of employee-generated content on social media engagement.