Social interaction can be a powerful strategy for persuasive technology interventions, yet many users are reluctant to engage with others online because they fear pressure, failure and shame. We introduce the 'ambivalent socialiser', a person who is simultaneously keen but also reluctant to engage with others via social media. Our contribution is to identify four approaches to introducing sociality to ambivalent socialisers: structured socialising, incidental socialising, eavesdropping and trace sensing. We discuss the rationale for these approaches and show how they address recent critiques of persuasive technology. Furthermore, we provide actionable insights for designers of persuasive technology by showing how these approaches can be implemented in a social media application.