Citizen science (CS) aims primarily to create a new scientific culture able to improve upon the triple interaction between science, society, and policy in the dual pursuit of more democratic research and decision-making informed by sound evidence. It is both an aim and an enabler of open science (OS), to which it contributes by involving citizens in research and encouraging participation in the generation of new knowledge. This study analyses scientific output on CS using bibliometric techniques and Web of Science (WoS) data. Co-occurrence maps are formulated to define subject clusters as background for an analysis of the impact of each on social media. Four clusters are identified: HEALTH, BIO, GEO and PUBLIC. The profiles for the four clusters are observed to be fairly similar, although BIO and HEALTH are mentioned more frequently in blogposts and tweets and BIO and PUBLIC in Facebook and newsfeeds. The findings also show that output in the area has grown since 2010, with a larger proportion of papers (66%) mentioned in social media than reported in other studies. The percentage of open access documents (30.7%) is likewise higher than the overall mean for all areas.