In this paper, we investigate personality expression and impression formation processes in online social networks (OSNs). We explore whether, when and why people accurately judge others' personalities (accuracy), successfully manage the impressions that others form of them (impression management) and accurately infer others' impressions of them (meta‐accuracy) at zero acquaintance. On the basis of targets' OSN profiles (N = 103), overall perceiver impressions were collected and compared with targets' self‐view, desired impression and meta‐perception. In addition, independent groups of thin‐slice perceivers based their personality impressions solely on one of four kinds of information within the OSN profiles (profile picture, interests field, group list and notice board), and more than 300 OSN cues (e.g. attractive person and number of friends) were coded. Results showed evidence of accuracy, impression management and meta‐accuracy, but their extent was moderated by the trait (e.g. Big Five and self‐esteem), the kind of information and the interplay of trait and information. Findings could be explained by cue expression and cue utilization processes (lens model analyses). Future prospects for studying personality impressions in online and offline environments are discussed. Copyright © 2013 John Wiley & Sons, Ltd.