11. A computer program product for determining social proximity between users of an online system, the computer program product comprising a non-transitory computer-readable storage medium containing computer program code for: accessing a profile of a user of the online system maintained by each of a plurality of social networking systems, each profile specifying a first plurality of additional users of a social networking system connected to the user via the social networking system; identifying a user of the first plurality of additional users of an identified social networking system; identifying a second plurality of additional users of the identified social networking system connected to both the user of the online system via the identified social networking system and to the identified user of the first plurality of additional users; generating a social proximity score based at least in part on a number of users in the second plurality of additional users connected to the identified user of the first plurality of additional users, the social proximity score indicating a relative social proximity of the user of the online system to the identified user of the first plurality of additional users; and recommending a content item to the user of the online system based at least in part on an interaction of the identified user of the first plurality of additional users with the content item and the generated social proximity score.
11. A computer program product for determining social proximity between users of an online system, the computer program product comprising a non-transitory computer-readable storage medium containing computer program code for: accessing a profile of a user of the online system maintained by each of a plurality of social networking systems, each profile specifying a first plurality of additional users of a social networking system connected to the user via the social networking system; identifying a user of the first plurality of additional users of an identified social networking system; identifying a second plurality of additional users of the identified social networking system connected to both the user of the online system via the identified social networking system and to the identified user of the first plurality of additional users; generating a social proximity score based at least in part on a number of users in the second plurality of additional users connected to the identified user of the first plurality of additional users, the social proximity score indicating a relative social proximity of the user of the online system to the identified user of the first plurality of additional users; and recommending a content item to the user of the online system based at least in part on an interaction of the identified user of the first plurality of additional users with the content item and the generated social proximity score. 13. The computer program product of claim 11 , further comprising computer program code for: monitoring an interaction of the identified user of the first plurality of additional users with respect to a content item in the online system; and recommending the content item to the user of the online system based at least in part on the generated social proximity score.