Background:
The tobacco industry was quick to exploit social media to subvert tobacco advertising and promotion bans, and directly connect with consumers. Social media offers similar opportunities for tobacco control, however evidence for how to effectively use it to influence behaviour is limited. The aim of this study was to understand how traditional mass media and peer influence approaches may need to be adapted for Facebook-based strategies.

Methods:
Community-based Indigenous peer researchers who were active Facebook users were recruited to share tobacco control content weekly from January to June 2017. Peer researchers were given three content options each week, and required to share at least one. They documented reasons for their choice and recorded both online and offline interactions it generated. Contacts from within the peer researchers' networks were interviewed face-to-face to understand the real world impact of the content, particularly posts which generated no online interaction. Data was inductively analysed using grounded theory methodology.

Results:
Messages which were direct, positive, specific and relatable for Aboriginal people's values and social context, and which had practical information were favoured. Content that leveraged people's care and concern for children was most likely to be shared, even if the content was international. The impact on peer researchers' Facebook contacts varied significantly. Some reported never seeing the content; others were directly impacted - including quitting smoking as a direct result of posts.

Conclusions:
The popularity of a Facebook post, as measured by visible reactions such as likes, shares and comments, does not necessarily equate with its real world impact. Shocking and graphic tobacco control messages used for traditional mass media campaigns are often bypassed or ignored by both smokers and non-smokers when sharing content on Facebook. Further research is required around the impact of tobacco control campaigns which are strengths-based and target Indigenous people.