Anti-slavery organisations utilise social media, particularly Facebook, to raise awareness of the problem of modern slavery and build support for efforts to combat this persistent human rights abuse. This research identifies the three significant obstacles organisations face when trying to engage and mobilise individuals to participate in antislavery activism. The organisations’ perceived credibility with Facebook users, the alignment of content to Facebook users’ information needs and the style of the posts influence how individuals engage with and act on the post content. This research finds that to encourage increased participation and interest in the modern slavery cause, anti-slavery organisations must enlist strategies to build their reputation and credibility with Facebook users and provide information to direct active participation in the cause at the individual and collective levels.