Social media are frequently touted for their potential to strengthen democratic processes by bringing politicians and citizens into dialogue with one another. Social media may enrich the public sphere and improve democratic decision-making by allowing politicians and constituents to discuss matters of political import directly, free from intermediaries. But what factors impact whether this potential is realized? Previous research has focused on politicians’ structural incentives for strategic communication online but neglected the impact of citizen demand for politicians’ attention. I examine the role of citizen demand using an original dataset comprising the Twitter activity from and to members of the lower legislative houses in the Netherlands, United Kingdom, and United States during the latter half of October 2013. The data suggest that citizen demand plays a crucial role in determining the presence, as well as the extent, of politicians’ reciprocal engagement with members of the public.