Research on the relationships between social media use and loneliness has produced mixed findings, in part because people use social media in different ways. Finsta is a private Instagram account followed only by a small group of the user’s friends and is considered to be a more authentic form of social media. The purpose of the present study was to examine the differential associations of Instagram and Finsta use with social and emotional loneliness and to investigate off-line engagement as a potential mediator of these associations. With data from an online survey given to N = 330 emerging adults, a series of hierarchical linear regressions showed that Instagram use negatively predicted and Finsta use positively predicted social loneliness, whereas neither were associated with emotional loneliness. Furthermore, whereas Finsta use was not associated with off-line social engagement with friends (OSE-friend), Instagram use was positively associated with this variable. In addition, results showed that off-line social support with friends partially mediated the relationship between Instagram use and social loneliness. The findings imply that all social media are not created equal; even within the same platform (Instagram), differential associations were found with social loneliness depending on the type of account used.