Influencer marketing, (also Influence Marketing) is a form of marketing that has emerged from a variety of recent practices and studies, in which focus is placed on specific key individuals (or types of individual) rather than the target market as a whole. It identifies the individuals that have influence over potential buyers, and orients marketing activities around these influencers.
Influencers may be potential buyers themselves, or they may be third parties. These third parties exist either in the supply chain (retailers, manufacturers, etc.) or may be so-called value-added influencers (such as journalists, academics, industry analysts, professional advisers, and so on).
The first approach to that theory comes from a communication´s classic "The people´s choice" a Lazerfeld and Katz 1940 study on political communication that was also known as Multistep flow model that claims that the majority of people are influenced by secondhand information and opinion leaders.
Read more about Influencer Marketing: What Is “Influence”?, Influencer Marketing As A Marketing Discipline, Identifying Influencers, Influencer Ecosystems and Roles