1. A system comprising: a computing device; and a non-transitory computer-readable medium coupled to the computing device and having instructions stored thereon which, when executed by the computing device, cause the computing device to perform operations comprising: receiving an identifier associated with a user of a social networking service provided by a first service provider; identifying, based on the identifier, one or more first services that the user uses, the one or more first services being provided by a second service provider and being different from the social networking service; identifying first contacts of the user within each of the one or more first services, one or more contacts of the first contacts being identified based on one or more of a private link and a network link between contacts; generating a social vicinity index based on the first contacts, the social vicinity index comprising one or more potential contacts for the user within the social networking service; transmitting instructions to display graphical representations of respective potential contacts of the one or more potential contacts to the user in a user interface of the social networking service; and receiving a user selection of a potential contact of the one or more potential contacts through the user interface of the social networking service, and in response, providing the potential contact as an actual contact of the user within the social networking service.