1. A method comprising: identifying a first user profile referenced by an action initiated by a first user; determining a similarity score that indicates a degree of similarity between the first user profile and a second user profile that describes a second user; accessing a volatility score that indicates a likelihood that the second user is receptive to a proposal that the second user be employed by an employer; determining a rank of the second user profile based on the similarity score and on the volatility score, the determining of the rank being performed by a processor of a machine; and presenting the second user profile to the first user based on the rank.