Anthropogenic marine debris (AMD) is a global problem and the identification of its sources is essential for adequate mitigation strategies. Herein we examined whether AMD density and composition differed between two countries with contrasting socio-economic backgrounds and marine litter sources (i.e. Chile and Germany). In nationwide beach litter surveys, we used a citizen science approach with schoolchildren and their teachers. Litter densities were substantially higher in Chile than in Germany. The different geographic zones surveyed in both countries showed strong grouping tendencies according to their main economic activities (tourism, shipping, fisheries/aquaculture), major litter sources, and AMD composition, in terms of dominance and diversity of AMD types. The results suggest that beach litter composition can be used as a simple proxy to identify AMD sources, and also that law enforcement and education can help mitigate the problem; however, for efficient solutions, production and consumption of plastics must be reduced.