<p>This paper examines the impact of social capital on advertising performance in an online social network. Specifically, we show that a widely-employed measure of social capital—network constraint—explains variation in the number of click-throughs received by 5986 banner advertisements appearing on 25 Twitter-related websites. As predicted, banner advertisements receive significantly more clicks when placed on websites that bridge structural holes, <em>i.e.</em> bridge otherwise disconnected segments of the network.</p>