In order to address the complexity of the modern social problems and needs through effective public policies, government agencies have started experimenting with policy informatics methods, adopting various approaches that increase citizens’ and stakeholders’ participation in the public policy formulation processes. Such approaches allow the exploitation of their opinions, which incorporate valuable perceptions of them, as well as knowledge, proposals and ideas. This paper outlines three advanced methods of social media (SM) exploitation in public policy making processes for citizen-sourcing, which are based on the concepts of active citizen-sourcing, passive citizen-sourcing and passive expert-sourcing respectively, as well as the conclusions from some first applications of them. Based on them a comparison of these methods is conducted, and then a maturity model is developed concerning the use of SM for citizen-sourcing in order to support policy making.