Understanding the personality-contextual attributes of target users can help developers design tools that increase the effectiveness of social media sites or identify appropriate lead users to seed products already in development. This paper illustrates that users' personality traits serve as a distinguishable set of characteristics that can be meaningfully related to YouTube usage. A model outlining the structural relations among: personality and motives (predictors), involvement (mediator), and video preferences and user activities on YouTube (dependent constructs) was proposed and successfully tested. The analysis was able to capitalize on the full statistical advantage of structural equation modeling in testing the unattenuated effects of the constructs through the use of fully latent variables. In particular, through the use of the new exploratory structural equation modeling technique, a full set of Big Five personality factors was modeled as latent variables – which was not methodologically viable until recently. Modeling a fuller set of predictors allows researchers to control for the influence of non-salient predictors and to ascertain the unique and common variances among predictors. Each of the Big Five personality factors was found to have a significant influence on at least one aspect of user participation. Extraversion and openness to experience had the most number of significant effects, showing not only proximal effects on motives but direct effects on video preferences and user activities as well. Although the effects of the other personality factors — neuroticism, conscientiousness, and agreeableness — were limited to motives, they were moderately stronger than extraversion and openness to experience.