I am not a lawyer but I think you would have to get the version of the agreements you had to click through in order to create an account and let a lawyer review them to see what you may have waived or what promises they made. After that your lawyer would have to prove damages and get a court to hear the case.
I don't remember agreeing to anything when signing up, but the damages are that my posts are now associated to my account. It's pretty hard to put a dollar amount on that, but I definitely think that it is damages.
You agree when you create your account. It's implied: "Using our services you agree to the terms and conditions which btw we can always change as we please and when we want" sadly.
Will you gain anything? Unlikely.
Why?
Historically these sort of lawsuits require you to have material damages in order to get anything. Have you been materially damaged?