Large amounts of personal data are generated through young people’s engagements with mobile media, with these data increasingly (re)used by advertisers, content developers and other third parties to profile, predict and position individuals. This has prompted growing concerns over the ability of mobile media users to develop informed stances towards how and why their data is being used, i.e. to build ‘conscious’ and/or ‘resistant’ forms of ‘data agency’. This paper explores ways of developing the critical consciousness and resistant practices of young mobile media users towards personal data. Drawing on research with 27 young people (aged 13–17 years), the paper describes efforts to make representations of third party use of personal data openly available as a basis from which to develop data-savvy tactics and strategies. The results of these interventions – while only partially successful – offer valuable insights into the technical, social and cultural issues that shape young people’s engagement with personal data. The paper concludes by considering how concerns over data agency might be better aligned with the realities of young people’s mobile media use.