The emergence of new media, devices, narratives and practices has compelled media literacy scholars and professionals to review their theoretical frameworks and methodological approaches. Based on a new conception -- 'transmedia literacy' -- that moves from traditional media literacy to informal learning and participatory culture practices, the research program behind the present article aims to understand how new generations are doing things with media outside schools and how they learnt to do the things they do. The article begins by describing the transformations of media literacy in recent years as a consequence of the mutations of the media ecology and, in that context, proposes a methodological approach for analysing the acquisition of transmedia skills by teens in informal learning environments. The article describes, analyses and evaluates the development and initial implementation of this methodology working with teenagers in a high-school in Barcelona. It ends with a Research Kit that includes surveys, creative workshops, interactive interviews and media diaries with teens between 12-18 years old. The article also describes the evolution of this methodological approach from its original formulation to the evaluation of the model after it was tested, and reflects on the possibilities of developing specific research devices to be applied in transnational research.