This two-volume set LNCS 11578 and 11579 constitutes the refereed proceedings of the 11th International Conference on Social Computing and Social Media, SCSM 2019, held in July 2019 as part of HCI International 2019 in Orlando, FL, USA. HCII 2019 received a total of 5029 submissions, of which 1275 papers and 209 posters were accepted for publication after a careful reviewing process. The 81 papers presented in these two volumes are organized in topical sections named: Social Media Design and Development, Human Behaviour in Social Media, Social Network Analysis, Community Engagement and Social Participation, Computer Mediated Communication, Healthcare Communities, Social Media in Education, Digital Marketing and