Whilst many studies have looked at the characteristics of effective communications via social media platforms, their use during public events for people to communicate and organize is still relatively uncharted. We have even less understanding of the roles that public event participants play in their use of social media, and this study seeks to address this gap in our knowledge. We analyse the Twitter data related to the 1st May 2014 event (Labour Day) in Germany to identify participant roles in this event, and the impact their tweets had on other participants. From this analysis we draw some tentative conclusions about participant roles in public events and their impact and highlight areas for further investigation.