The emergence and explosive growth of social media platforms such as Instagram, Facebook, Tweeter, etc. has dramatically changed both the way consumers shop and brands advertise. According to a study by Track Maven, Instagram is the most engaging social media platform nowadays with the most average interactions per post per 1,000 followers. It stimulates “Instagram influencer marketing” to develop rapidly and promotes a great variety of brands. It has fundamentally changed the balance of power between customers and brands because it allows peer recommendations to play a much larger role in purchasing decisions [13]. It has become one of the trendiest marketing strategies that focus on influential figures on Instagram rather than targeting on the market as a whole. Instagram influencer marketing highlights content creators who may impact their audiences’ buying habits. For example, shoppers who compare hotel reviews can simply search “hashtag plus hotel name (e.g. #hiltonnewyork) in Instagram and read people’s experiences with that hotel among related posts. Many of those posts were created by influencers who are collaborating with the brands to advertise. Based on activities of more than 12 million Instagram influencers between the first quarter of 2018 and the first quarter of 2019, Social bakers created a report to categorize influencers into three categories: micro-influencers who have fewer than 10,000 followers, macro influencers with 10,000 to 50,000 followers, and celebrities who attracts a million or more followers. The majority of Instagram influencers are “micro-influencers”. Their finding also reveals that the combined amount of sponsored content on Instagram for all three categories of influencers in North America has jumped 150% in the last year.

ABSTRACT
    Introduction
    Study 1 The Impact of Influencer’s Number of Followers and Expertise
    Study 2 The Impact of Expertise and Posting Features
    Preliminary Results

• Yanni Ping(St. John's University, United States) Corresponding author
• Lei Song(Penn State Abington, United States)