Methods and systems for selecting and presenting a content item, such as an advertisement, to a user of a social network are provided, where the content item is selected based on a calculated “content propagation likelihood” for the user. A user's “content propagation likelihood” is a likelihood that an entity (e.g., video, audio clip, photograph, etc.) will spread throughout the user's social network, and the social networks of the user's friends, when the entity is shared (e.g., broadcast) by the user. A user's content propagation likelihood is computed using weighted measures of various ways in which an entity can spread through a social network. A user's content propagation likelihood may also be set for a given vertical (e.g., music, sports, etc.) and/or a given media type (e.g., images, videos, etc.) that pertains to the particular user.