Here is my advice to you, maybe it will help you.
1) Change all passwords & emails immediately.
Create a brand new password and register new email accounts for different sites. Depending on the importance of the account create a password anywhere from 9 to 30 characters long using both uppercase/lowercase letters, symbols and digits.
Refrain from using the same email and password combination on more than 1 site. Often people like this will attempt to use your account info on other sites to see if it matches.
Make sure you have strong passwords on your email accounts. With an email account an attacker can reset passwords on any account associated with it and won't ever have to bother trying to h4c|< you.
I know having long and complicated passwords and multiple email accounts can be hard to remember. If you want, I can teach you how to keep a record of all your accounts that is locked and safe without 3rd party software or paying anything.
2) Keep your accounts free of private information
I know it's difficult to do while still being social but refrain from putting any personal identifiable information on any of your accounts. This includes real life photos, names, dates, addresses, interests and even gender of yourself and everyone you know. These type of things can be used by an attacker to build an online profile of you that he can use to blackmail, h4c|< and attack you with as well as use to social engineer people.
3) Keep records of everything.
Screenshot every message you receive from him no matter where its from. Take screenshots of the avatar card and homepage of every IMVU account he uses whether its stolen or not. Record every username, email, IMVU account name etc.. that he uses to engage with you.
This information can be used as evidence for authorities and an online profile for h4c|<7r. It will also help you learn to spot this guy when you meet someone new.
4) DO NOT interact with him.
Do not reply back to his messages. Do not try to plea, bargain or threaten him. That will do nothing but give him more reason to come after you and cause you more stress.
5) Block / Report him
Every major social networking platform has a way of blocking and reporting someone. Every time he contacts you use the block & report feature immediately.
Sometimes #4 and #5 are enough to get someone to leave you alone, they end up getting bored or it becomes too much trouble to continue getting new resources to attack you with.
I know a lot of my advice may seem difficult, time consuming or even unwanted but when you're in a situation as serious as this you have to take drastic measures. I hope what I have said helps you. If you need further assistance let me know.