Any easiest method to follow social media bounty campaigns? 
Keep an eye on this.
https://bitcointalksearch.org/topic/overview-of-bitcointalk-twitter-campaigns-last-update-11-august-2017-1771802
Be active in the marketplace section as well as service announcements section. You will be able to find all of them.
Bookmark the ones you have joined and just check once daily.
But do you know any similar sources about facebook bounty campaigns?
Yeah that's right. I always check in marketplace, what I do is turn on the notification for the said thread then when I check my email Boom! That's it a bounty campaign 😃