Mobile social networking sites (SNS) are frequently theorized to lead to perceived information overload, which may affect the well-being of individuals in negative ways. However, the available body of research is mainly based on cross-sectional data. Based on the limited capacity model of motivated mediated message processing (Lang, 2002), we tested the over-time relationships between mobile SNS use, information overload, depressive symptoms, and well-being in a two-wave panel study. Using a quota sample of adults (NT2 = 461), we found that YouTube use increased perceived information overload for all individuals. WhatsApp and Snapchat use did only lead to perceived information overload for older adults. Facebook as well as Instagram use were unrelated to perceived information overload. Furthermore, perceptions of information overload were a significant predictor of depressive symptoms, which in turn, negatively influenced individuals’ well-being over time. Implications of these findings are discussed.