In this paper, we propose a research model of the continuance of usage intention of a social networking site (Facebook) based on the theory of planned behavior and taking into account users’ gender and their perceived shyness degree. Our findings suggest that for men and women alike, the continuance of usage intention is determined by the attitude and the perceived behavioral control (PBC). Both hedonic and utilitarian outcomes are important to shape the users’ attitude towards Facebook. While non-shy people (male and female) behave exactly the same and are only led by attitude to decide to continue using Facebook, for shy people, the gender effect seems to be significant in shaping the attitude towards the SNS and in determining the role of PBC: for shy men, the decision to continue using Facebook is only affected by PBC whereas for shy women both attitude and PBC are important. For all the categories of users considered, social influence does not play any significant role.