To understand who uses social media and how often they do so, we examined the personality traits that predict frequency of using a set of 10 different types of social media (e.g., social networks, blogs, virtual worlds). Using survey data collected from two large-scale samples of young adults (Exploratory Study 1 N = 1586, Confirmatory Study 2 N =1432), we conducted direct replications of our findings to test whether the observed relationships between social media use and personality traits were reliable. Our replicated findings reveal that sex, age and extraversion are reliable predictors of several types of social media use (e.g., Facebook, Messaging Platforms, Online Forums), while other traits (e.g., agreeableness, Machiavellianism) showed unreliable associations. Our findings also reveal dimensions of multiplatform social media use that categorize the media ecologies of young adults and show significant associations with individual difference measures. (C) 2020 Published by Elsevier Inc.