We combine philosophical theories with quantitative analyses of online data to propose a sophisticated approach to social media influencers. Identifying influencers as communication systems emerging from a dialectic interactional process between content creators and in-development audiences, we define them mainly using the composition of their audience and the type of publications they use to communicate. To examine these two parameters, we analyse the audiences of 619 Instagram accounts of French, English, and American influencers and 2,400 of their publications in light of Girard's mimetic theory and McLuhan's media theory. We observe meaningful differences in influencers' profiles, typical audiences, and content type across influencers' classes, supporting the claim that such communication systems are articulated around 'reading contracts' upon which influencers' image is based and from which their influence derives. While the upkeep of their influence relies on them sticking to this contract, we observe that successful influencers shift their content type when growing their audiences and explain the strategies they implement to address this double bind. Different types of contract breaches then lead to distinct outcomes, which we identify by analysing various types of followers' feedback. In mediating social interactions, digital platforms reshape society in various ways; this interdisciplinary study helps understand how the digitalisation of social influencers affects reciprocity and mimetic behaviours.