If you filed a police report, then the police will investigate and, depending on the type of crime and what they discover, they will either turn their gathered evidence over to the prosecutor, who will determine what charges, if any, to file against the online poster, or the police will turn your complaint over to the local FBI office's computer crime division to investigate.
The FBI's computer crime unit becomes actively involved in internet crimes when there are serious online threats, or when there is evidence of child exploitation or child pornography. These crimes will take priority over most cyberbullying and harassment and misdemeanor stalking cases that occur with some frequency online (although these, too, will be investigated).
If you are a minor and the postings are sexual in nature, this may be given some priority, depending on the content of the postings.
What happens with the police/FBI case is now pretty much out of your hands. They will give your complaint the attention it deserves. If or when charges are filed against the online poster, the online poster will be notified of the charges and court action will proceed against him.
Often faster than waiting for the authorities to act on an internet case is to hire an attorney and pursue a civil action against the online poster, if the facts of your case can support such a suit. This is also, however, a more expensive route to take.
You can file a defamation action against your "John Doe" poster and, if your suit has merit, the court will issue a subpoena to the website that hosts the defamatory material and the online poster's identity can be revealed so the suit against him can proceed. As long as you file your defamation suit within the one year time frame, you can continue to pursue the action past this one year date.
When you know the identity of the online poster, it makes everything much easier. To identify an anonymous poster takes time, whether the police are investigating the complaint or whether you have an attorney working with you on a civil action. But if you wish to pursue a civil action, you must keep in mind the one year time frame within which you must file such an action.