Communication through social media is becoming more prevalent in dynamics of coordination and information diffusion. However, online networks are so large and complex that we require new methods to summarize their structure and identify nodes holding relevant positions. We propose a method that generalizes the sociological theory of brokerage, originally devised on the basis of local transitivity and paths of length two, to make it applicable to larger, more complex structures. Our method makes use of the modular structure of networks to define brokerage at the local and global levels. The findings show that the method is better able to capture differences in communication dynamics than alternative approaches that only consider local or global network features.