In addition to search engines, social networks represent an important digital service for many Internet users. Social network services such as Facebook, Xing, or Twitter provide vital platforms for communication and sharing of content as part of a modern, user-friendly Internet. Public criticism of social networks is expressed in particular with regard to processing of personal data. These play a central role in business models of many social networks, with regard to their use e.g. for advertising purposes. A question is, if it can be assumed that market-dominant providers, due to a lock-in effect, can demand a wide-ranging consent for the collection and use of personal data that would be expected in a functioning competition? In the following, social networks, potential competition issues and possible legislative measures due to concentration tendencies in connection with access to user data in the area of social networks will be discussed.