Interaction between candidates and constituents via social media is a well-studied domain. The article takes this research further through a synthesis with platform studies, emerging scholarship that applies a critical perspective to the role of digital platforms in society. Examination of candidate–constituent interaction via Twitter and Facebook during the 2015 Finnish parliamentary elections revealed that the types of interaction differ between the two platforms: Facebook was used for formal campaigning and for praising and expressing support, while Twitter was utilized for information and for seeking and sharing opinions. An additional finding is that interaction approaches may be platform-specific, with socio-emotional functions being employed more often by candidates than constituents on Facebook while no such difference existed for Twitter. On the basis of the implication that platforms have a critical role in the nature of candidate–constituent social media interaction, we discuss the implications of platformed interaction for the democratic process, suggesting that campaign strategy may exploit it in ways that may even necessitate regulation. Furthermore, scholars of social media interaction might need to consider the broader ramifications of the findings, and contributions to theory that acknowledge platforms’ part in interaction may be needed.