Find Out How to Search Every Social Media Site for Any Subject

I would like a description/procedure for how to search for accounts on a given subject (for example politics or baseball) on each of the following social media sites. With the description, show it being used to find MATHEMATICS accounts with jpeg snips and words describing each step.

1 Facebook
2 Youtube
3 WhatsApp
4 Messenger
5 WeChat
6 Instagram
7 TikTok
8 QQ
9 Qzone
10 Sina Weibo
11 Pinterest
12 Tumblr
13 Reddit
14 Twitter
15 LinkedIn
16 Douban
17 Baidu Tieba
18 Snapchat
19 Viber
20 Discord
21 Vimeo
22 Telegam
23 Line
24 Twitch
25 Medium