  Social media provides the means by which extremist social movements, such as
white supremacy and anti LGBTQ, thrive online. Yet, we know little about the
roles played by the participants of such movements. In this paper, we
investigate these participants to characterize their roles, their role
dynamics, and their influence in spreading online extremism. Our participants,
online extremist accounts, are 4,876 public Facebook pages or groups that have
shared information from the websites of 289 Southern Poverty Law Center
designated extremist groups. By clustering the quantitative features followed
by qualitative expert validation, we identify five roles surrounding extremist
activism: educators, solicitors, flamers, motivators, sympathizers. For
example, solicitors use links from extremist websites to attract donations and
participation in extremist issues, whereas flamers share inflammatory extremist
content inciting anger. We further investigate role dynamics such as, how
stable these roles are over time and how likely will extremist accounts
transition from one role into another. We find that roles core to the movement,
educators and solicitors, are more stable, while flamers and motivators can
transition to sympathizers with high probability. We further find that
educators and solicitors exert the most influence in triggering extremist link
posts, whereas flamers are influential in triggering the spread of information
from fake news sources. Our results help in situating various roles on the
trajectory of deeper engagement into the extremist movements and understanding
the potential effect of various counter extremism interventions. Our findings
have implications for understanding how online extremist movements flourish
through participatory activism and how they gain a spectrum of allies for
mobilizing extremism online.
