Social commerce (s-commerce), the use of social media to support e-commerce, has become pervasive nowadays. This paper aims to investigate into an important type of consumer behaviour that could generate considerable economic values for s-commerce: impulsive purchase. Specifically, we focus on the role of peer influence. Based on social influence theory, the process via which a consumer changes a peer’s behaviour is interpreted along two dimensions: informational and normative. To further explore the factors which lead to these influencing processes and impulsive consumptions, the reflective-impulsive model of consumer behaviour is adopted, which suggests that peripheral cues decide impulsive behaviour. As a result, a research model connecting peripheral cues with influencing processes and impulsive behaviour is proposed. Via a survey of Sina Weibo users, 303 responses were obtained to empirically teste the model. The results indicate that consumers’ expertise and trustworthiness are significantly related to both types of social influence they could exert on peers. Further, the s-commerce system’s support for personalization and social interaction could notably facilitate consumers’ exchange of social support, and therefore significantly facilitate social influence.