<jats:sec> <jats:title>Purpose</jats:title> <jats:p>In order to improve advertising target accuracy, e-commerce platform (e-platform, for short) and social platform (s-platform, for short) try to share consumer information via social login which is widely adopted by e-platforms. If consumers choose social login, they can use an s-platform account to log in the e-commerce platform. Within social login, depending on who decides the amount of shared information, there are two information-sharing modes: consumer-led information-sharing mode (CI, for short) and e-platform-led information-sharing mode (PI, for short). On the other hand, consumers concern over the sharing of their information, which in known as privacy concern. This paper aims to analyze the optimal information-sharing strategy considering consumer privacy concern within social login when the platforms target advertising with consumer information.</jats:p> </jats:sec> <jats:sec> <jats:title>Design/methodology/approach</jats:title> <jats:p>This paper constructs a game theoretical model to study information-sharing strategies in a market composed by an e-platform, an s-platform, a firm and a unit of consumers. Under different modes, the equilibria of the information sharing strategy and the e-platform’s profit are derived. By comparing the equilibria, the optimal information-sharing mode selection strategy is given.</jats:p> </jats:sec> <jats:sec> <jats:title>Findings</jats:title> <jats:p>The results show that if the privacy concern adjustment coefficient is low, when the advertising targeted accuracy is low, CI is optimal for the e-platform; otherwise, PI is optimal. If the privacy concern adjustment coefficient is high, when the advertising targeted accuracy is mediate, CI is optimal for the e-platform, otherwise, PI is optimal. Moreover, when the privacy concern adjustment coefficient is high, part of consumers will authorize the e-platform to share all their information, the rest consumers will not authorize the platform to share the information; when the privacy concern adjustment coefficient is low, all consumers will authorize the platform to share all their information. Finally, when the advertising targeted accuracy is low, the e-platform and s-platform will share all consumer information; when the advertising targeted accuracy is high, the e-platform and s-platform will not share consumer information.</jats:p> </jats:sec> <jats:sec> <jats:title>Originality/value</jats:title> <jats:p>This paper provides insight into the inter-platform information sharing strategy via social login considering consumer privacy concern when the platforms target advertising based on consumer information. It can help the e-platform to choose proper information-sharing mode and help consumers and platforms set information-sharing strategy in practice. In addition, this research provides a supplement to the research on social login and information sharing on the theoretical level.</jats:p> </jats:sec>