Homeless crack users are an important segment of the population living in extreme vulnerability in Brazil. In 2011, the Consultório na Rua - CnaR (Street Clinic) was created, to improve access to health care for this population. Considering building up social support networks as a strategy to face life's difficulties, this study aims to analyse how crack users, in Rio de Janeiro, relate to territory and build social support networks to deal with their everyday life challenges and health needs. We carried out in-depth interviews with 10 homeless crack users assisted by CnaR and 11 health professionals; one Focus Group with 6 users, and Participant Observation of CnaR's work during 2014-2016. Methodology was based on the use of an analytical matrix with theoretical and empirical categories of "Territory", "Territoriality", "Social Support Networks" and "Gift". Results revealed crack users' territorialities, alternating moments of concentration and disaggregation with high geographical mobility, except in periods of strong consumption of crack. Territorialities are unstable, marked by violent Police repression. In spite of the stories of losses and ruptures, forms of sociability among users and CnaR professionals were identified, as well as with different actors in the territory. All this favoured the formation of supportive networks providing friendship, health care, and other material and symbolic goods. The systematization of the users' informal networks, usually invisible to workers and administrators, is relevant because of its potential to expand the production of care and strengthen the associations in the territory. To understand users' territorialities and the social support networks formed in their everyday life is not only innovative, but also contributes to the formulation of public policies that aim to guarantee civil rights to people in a situation of vulnerability, suffering and social exclusion.