Social media offers individuals and organisations new opportunities for speaking up. The receiver's valuation of the sender's voice is a prerequisite for resulting change. However, the influence of modern communication channels like social media on this valuation has not yet been investigated. Against this background, our study investigates the valuation of social media voice. We conduct a scenario-based experiment in which the participants imagine themselves to be a manager who is evaluating a proposal. The results show that the valuation of voice is better if a proposal is communicated via voicemail than if it is communicated via social media, if the proposal is based on the opinion of an individual rather than that of a group, and if the source is an expert. We also find a three-way interaction between the channel, source, and source credibility. The paper provides contributions to research on employee voice, the ELM, and the Social Presence Theory. We discuss our findings and derive opportunities for future research and implications for both employees and organisations.