Social networks such as Facebook and Twitter are privileged platforms for teenagers’ expression and information sharing. This study, based on a Big Data approach, aims to explore how persons under 18 years old “talk” about their mobility behaviors and aspirations on these social networks. This exploratory research analyzes millions of public posts (“tweets”) from Twitter in order to identify relevant topics related to the topic “mobility under 18”. This exploratory work generated insights for the design of a web quantitative survey done by the EPFL Laboratory of Urban Sociology (LaSUR).