With the rise of internet celebrity economy and the rapid development of diversified social media platforms, influencer marketing, as a new and efficient marketing strategy, has triggered a marketing revolution. The influencers mentioned in this article refer to internet celebrities who are famous for self-building by sharing creations on social media platforms, such as food bloggers, beauty bloggers, and social media streamers. They establish a huge fan base and regard online social activities as a profession, which have a huge influence. The information provided by these social media influencers is easier to reach the target audience, is easier to be spread virally, and is often not perceived as a purely commercial drive and easy to be trusted by fans, so they have a natural marketing advantage. In recent years, more and more businesses have begun to use these influencers to endorse their products or services, hoping to influence the attitudes and decisions of consumers, thus forming an efficient new marketing method of influencer marketing. However, the academic research on influencer marketing is still in its infancy, and influencer marketing practice has phenomena such as cognitive errors, neglect, blind obedience, and excessiveness, which urgently need scientific and professional guidance. In view of this, this article provides a review of the literature on the topic of influencer marketing.

This article provides an overview of existing domestic and foreign research on influencer marketing. First, we delineate the keyword co-occurrence and research field co-occurrence of existing researches to present current research status. Then, we interpret the development context and research paradigm of influencer marketing theory. Further, we analyze the connotation of influencer marketing, interpret the characteristics of social media influencers as information sources, summarize different types of social media platforms used by internet celebrities, and sort out the application scope of influencer marketing. In addition, we interpret the theoretical model of influencer marketing mechanism from the perspective of trust and user identification, and propose an integrated research framework based on quasi-social relations. This is a relatively comprehensive and overall outline of the existing influencer marketing mechanism research. Finally, we conclude with some directions worthy of attention for future research, and provide some ideas and references for influencer marketing practice.

The main contributions of this research are as follows: First, we review social media influencers（SMIs）and influencer marketing to distill the connotation of influencer marketing, clarifying the distinctive features of influencer marketing that are different from traditional marketing strategies such as eWOM and relationship marketing. Clear understanding of the essence of influencer marketing provides theoretical basis for influencer marketing practice. Second, we provide a systematic review of the specific applications of influencer marketing in advertising, brand management, word-of-mouth marketing, and customer relationship management. It sheds light on the influencer marketing strategy practice. Third, we develop an illustrative research framework of influencer marketing mechanism based on the mediating role of parasocial relationship and boundary conditions such as influencer endorsement and follower characteristics. It is the expansion of the research field of influencer marketing mechanism.