We consider a strategic online social network that controls information flows between agents in a social learning setting. Agents on the network select among products of competing firms of unknown quality. The network sells advertising to firms. We consider display advertising, which is standard firm to consumer advertising, and social advertising, in which agents who purchased that firm's product are highlighted to their friends. We show that in equilibrium, information is unbiased relative to a setting with no advertising. However, the network reduces the information agents see about others’ purchases, since this increases advertising revenue. Hence consumer welfare is lower than in the first best.

Joint work with Manuel Mueller-Frank