Social media apps like TikTok have influenced the daily lives of billions of users. Such apps are forms of network goods and subject to so-called network externalities. They offer a social utility that increases with the number of app users. Regarding its origin, the social utility can be divided into a strong-tie utility (STU) and weak-tie utility (WTU) as it may emerge from strong ties (e.g. close friends) and weak ties (e.g. friends of friends) respectively. To investigate their influence on the usage behaviour more closely, we develop a research model and conduct an online experiment (N=291) for collecting data for seven popular social media apps. The results prove that strong and weak ties can influence users in two ways: providing utility and exerting social pressure. While the level of these effects varies for the tested apps, the utility has a generally greater influence on the intention to use.