1. A computer-implemented method for determining user influence across an online social network, comprising: obtaining, via a processor, user data for at least a first user and a second user in a plurality of users of a social network; determining a first influence score representing a measure of influence of the first user on the second user, and a second influence score representing a measure of influence of the second user on the first user by generating, from the user data, a first influence vector for the first user and a second influence vector for the second user, wherein each of the first and second influence vectors is based on a profile vector characterizing a user on the social network and on an activity vector describing a type of activity performed by the user on the social network; building an influence graph of the plurality of users, wherein at least a first node and a second node in the influence graph correspond to the first user and the second user, respectively, and wherein edges connecting the first node and the second node correspond to the first influence score and the second influence score; identifying a path through the influence graph, the path having one or more of the plurality of users; and sending targeted data to the one or more users in the path.