1. An advertising targeting system configured to generate a set of targeting keywords that target a specific offer to a desired audience, the system comprising: a targeting server system comprising a network interface and a database; wherein the targeting server system is configured to: obtain a set of offer keywords comprising the attributes of at least one specific offer within an advertising campaign obtain a set of member profile data from at least one server that forms part of an online social network using the network interface, where a member profile in the obtained member profile data describes activities performed on the online social network associated with the member profiles; determine member profile affinity metadata for a subset of the set of member profile data, where the member profile affinity metadata describes the affinity of a member profile with respect to a set of specific keywords; generate a member affinity database stored using the database and containing the member profiles and the determined member profile affinity metadata; and identify targeting keywords within the specific keywords based on the offer keywords and the member affinity database by: clustering the member profiles within the member affinity database based on the member profile affinity metadata and the offer keywords; selecting at least one member profile cluster based on the affinity of the member profiles within the member profile cluster to at least one of the offer keywords; identifying at least one additional keyword within the specific keywords based on the affinity of the member profiles within the selected at least one member profile cluster to the at least one additional keyword; and determining a set of targeting keywords based on the offer keywords and the additional keywords.