In extreme events such as the Egyptian 2011 uprising, the online social media technology enables many people from heterogeneous backgrounds to join the event in response to the crisis. This form of collectivity (online crowd) is usually formed spontaneously with minimum constraints in the relationships among the members. The theories of collective behavior suggest that the pattern of behavior in the crowd is not just a set of random acts. Instead they evolve toward a normative stage. Because of the uncertainty of the situations people are more likely to search for norms. Understanding the process of norm formation in online social media is beneficial for any organization that seeks to establish a norm. In this study, we propose a longitudinal data-driven approach to investigate the process of emergent norm formation in online crowds in the context of the online crowd formed around the Egyptian Revolution in 2011.