People influence each other in the environment of social networking sites (SNS). Some SNS have gained popularity. Practitioners and researchers assume that these popular SNS are influential. However, influence and popularity are two different concepts. This research aims to provide two clear concepts of influence and popularity as well as their relationship. Popularity is hypothesised that it is affected by elements in the surroundings (e.g. societal position of a SNS owner) of SNS based on a peripheral information processing mechanism, whereas influence is hypothesised that it is affected by core elements (e.g. quality of content on a SNS message) of SNS based on a central information processing mechanism. The results indicate that influence is solely affected by the central information processing mechanism, but popularity is affected by both central and peripheral information processing mechanisms. There is a relationship between influence and popularity but it is marginal. Therefore, it should not be assumed that popular SNS are influential and vice versa.