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.