How to thank someone for following you back on social media?
谢谢你关注我呀！！！

There's actually an article that kind of talks about this on zhihu, funnily enough. Their translation there is:


  thank you follow me --> 谢谢你关注我呀！！！


They also have a picture of automated thanks for following me in action:


  


On social media 关注 is always the term for follow.