Social media have become an ever-present part of our lives and their impact is felt in many areas. The present paper focuses, in particular, on the way social media have redefined the concept of ‘celebrity’ with the arrival of so-called superusers, YouTubers and Instafamous personalities. Numerous studies have shown that present-day teenagers and young adults are more affected by these digital celebrities than traditional celebrities such as musicians, athletes, movie stars (e.g. in their purchase behavior as seen in Djafarova & Rushworth, 2017). One of the reasons why digital celebrities are so popular is that in their idols, teenagers are looking for somebody who shares their values, is their friend, and essentially ‘one of us’. In line with the communication accommodation theory (CAT), the present study argues that in order to achieve this friend-like status and eventually a large followership, users linguistically accommodate to their audience; in Goffman’s terms (1959), they attune their online performance to the expectations of their spectators. Attention in this paper is paid to communication on Instagram where the majority of users (more than 60%) is formed by Millennials. The speech of Millennials is characteristically described as informal and this demographic group is often thought to drive language change by breaking the norms of what is considered formal and informal in a given context. While informality is seen as the most essential element of youth talk on social media, the concept is still largely underdefined. In the spirit of the topic of this panel, the present study thus aims to shed more light on what it means to be informal online, in particular, on Instagram. The analytical data consist of posts extracted from five Instafamous profiles (i.e. followed by more than 500,000 users), saved with accompanying metadata (e.g. hashtags, tags, images). Using content analysis, the data have been searched for any recurrent features of informality. Since convergence concerns “a wide range of linguistic-prosodic-nonverbal features” (Giles, Coupland & Coupland, 1991, p. 7), visual and potentially also auditory elements have also been examined, leading to a multimodal analysis. The findings show that informality is most visible in the posts which are, according to the author’s novel classification model of Instagram posts, labeled as ‘private-like’. Moreover, since these posts usually depict user’s private life yet are, at the same time, publicly available, this study confirms the argument that the boundary between the front and back stage is blurred online.