MyBB Community Forums

I have been searching for a plug-in that replaces Private Messages with Private Threads, which are actual threads that can be posted in, but are private to the user. The user can invite other users to this Private Thread, and it will be available in their Private Thread list. They will be alerted whenever their is a new post in any Private Thread they are in. They can remove themselves from them. Only the person who started the Private Thread can lock it, change the title, and perform other special actions.

Can anyone help me find a plug-in like this? Does one even exist?

Thank you!