To get a subpoena you first need to file a law suit. You can file a law suit without a lawyer "Pro Se" (latin meaning for yourself), and you can then petition the court for the subpoena.
You will need to show the court items that go beyond free speach for them to consider issuing the subpoena.
This answer begs the question: Do you have a law suit? Have you been damaged? Damages generally refer to lost money. Can you show that?
As you can see, there is a lot more to this scenario than meets the eye. Look for a lawyer in your local who lists cyberlaw as an area they handle. You may want to discuss your situation with a lawyer in more detail. Most lawyers on Avvo offer a free phone consultation.
This post is provided for general informational purposes only and is not intended to be legal advice specific to you. This general information is not a substitute for the advice of an attorney in your jurisdiction. The attorney client relationship is not established by this post.