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On social networking sites, users are continuously exposed to a variety of posts from the networked individuals. Such information may often influence recipients’ perceptions of what is important and goal pursuits such as materialism. Even though several studies have examined the negative consequences of using social networking sites, less attention has been paid to the role of friends’ number and its impact on people’s life goal pursuits. This study aimed to investigate the dark side of online friends and explored why and when more friends in social networking sites would promote materialism. Based on a sample of 264 WeChat users, study 1 discovered that friends’ number positively impacted materialism through extrinsic goal (i.e., wealth and status). Additionally, such association was moderated by social comparison orientation and self-esteem. Importantly, self-esteem buffers the detrimental effect of friends’ number on materialism while social comparison orientation increases it. Study 2 further tested the causal relationship and showed that friends’ number on SNS might become a signal to indicate materialism via an experiment. In conclusion, our findings add to the understanding of psychological processes regarding the dark side of online friends’ number and render suggestions for developing positive personal value.