Modelling the liability of social platforms has become a pressing issue, along with emerging efforts to institutionalise the accountability of digital collective actors, including human-algorithmic associations. However, to make social platforms liable, it is necessary to resolve the problem of the accountability of private actors for human rights violations traditionally immune to human rights challenges because social platforms are owned by private actors, who also manufacture their contents and coordinate and control them. Different strategies are employed or offered to remedy the situation. Considering that human rights violations in the digital sphere are of ‘constitutional quality’, this chapter identifies the horizontal application of constitutional rights as a possible response to human rights challenges raised by the actions of social platforms. This step does not require the recognition of new rights but the recognition of new duty holders, such as social platforms, in relation to existing rights. The examples from Germany, Canada, and the European Union illustrate its promising potential to remedy online human rights abuses.