How do I go about suing these social media companies?
You're asking the wrong question.
Find the right lawyer
It's that simple.
Which lawyer has had success fighting against social media companies?
That's the question to ask.
He or she will help you find out if you have a case with any merit, find the "right" venue where a judge will be sympathetic to your case, and he/she will know HOW to plead, do the discovery and argue your case.