Affordances are action possibilities that emerge from the relationship between the properties of an object and an interacting agent’s capabilities. This poster examines how one type of affordance—anonymity—is enabled or constrained by six features of social media platforms. Our work is one step in a broader agenda to: (1) identify affordances that influence users’ behaviour in online communities; (2) outline the social media features that enable or constrain those affordances; and, (3) experimentally determine whether certain affordances, or combinations of affordances, support prosocial behaviour. Prosocial behaviour in information and communication technologies (ICTs) is broadly viewed here as benefiting other individuals in online communities, which in turn could increase the subjective well-being (SWB) of the community’s members. SWB is characterized by high positive affect, low negative affect, and high life satisfaction.