ANONYMITY: Who wrote that?
Anonymous free speech is a wonderful privilege protected under the US First Amendment.
However, malicious antagonists using anonymity to spread lies behind the cloak of anonymity are NOT protected by the First Amendment.
The U.S Congress, in all its wisdom, enacted a law that effectively grants Federal immunity to blogsite owners, forums, ISPs, search engines and any online service that "re-publishes" the libel. Even if you demonstrate to the ISP's board of directors the falsity, they can ask you to leave and do nothing to remove it from their servers.
A victim does not have many options, but here are a few tips that our team have used to help our clients.
Step1
Make sure you save regular copies of the offending-web page in case you need to demonstrate how long it was visible and any variations or changes. You can save the HTML file in most browsers by choosing FILE>>SAVE; using this method you can save all the associated files such as images etc.Step2
If the blog postings do not have the date/time stamp visible, you should note as accurately as possible the date it appeared. This may be needed for backyard blog site owners who may be subpoenaed. Many don't have good records or do not know how to read their logs.Step3
Journal / log all instances of lost business or expressions of concern about your character by individuals as a result of the libelous anonymous blog posting.Step4
If you notice similar patterns of writing styles with different blogger pseudonyms, be sure to keep detailed records, notes and cross-references. Often one person pretends to be many in an attempt to give the appearances of a grass roots uprising against you. This is called "astroturfing"; if you do end up in court this helps in proving "malice" which in some jurisdictions adds a whole new level to the damages that may be awarded.Step5
You cannot prevail in court if you litigate against an ISP or blog site administrator (except if he/she is the actual author of the libel). In order to identify an anonymous blogger you will probably need to file a "Your Name vs. John or Jane Doe" civil suit in the appropriate jurisdiction. Identifying the best jurisdiction can be tricky as some ISPs such as Google will usually only honor a court order from their state (California).Step6
Once you have filed an action you will need to have the court issue a subpoena, or in some cases an actual order for production. Many ISPs will resist this so it is imperative that you are very, very careful, thorough and yet concise in the justification/explanation for the production requests. I have learned by trial and error and have perfected the task in so much as it is possible. You need to find a balance between the techno-speak for the ISP's records team and plain English so the Judge doesn't get lost.Step7
Once you obtain the production/documents from the ISP you will probably need to request additional subpoenas for other ISPs as you track down the electronic foot prints of your antagonist. If you do everything just right, you will be able to positively identify all but the sneakiest of the cowardly minority that take pleasure in inflicting pain on us without a conscience. 
