YouTube: Youtube is popularly used for musicians to share and promote their music videos and their content to younger audiences from mostly 16- 35 year olds.
Instagram: Instagram is mostly used for up and coming musicians and producers to share videos in hope of reaching a large audience with their skills
Facebook: Facebook can be used to promote music to most of the older audiences such as 40 onwards. this is good for promoting music like reggae, ska and maybe blues music videos.