Eh, I guess this is not true. To me, 'social media' always meant websites like MySpace and Orkut where friends connect, and not just 'website where users can communicate in some way' a la Pinterest/Reddit/YouTube.

But I realise now that isn't the right definition... still not sure what the word is for the Friendster/MySpace clones--but among those I am pretty sure Facebook is more than 90% of the market (outside of China), possibly more than 99% with Google+ closing.

Facebook owns Instagram - the 2nd largest social network - as well as Whatsapp which is ginormous in its own right as well.

I'd guess mostly WeChat/Alibaba/TikTok, and a few tiny players that ebb and flow in impact.