communicator with user

Hello,

i need plugin or somethink to speak (no real time) in user on my website.

For example:

On website is 30 user and me(admin). I need to create ‘topic’ or chat where can i write to him somethink but another user can’t see this.

If i open chat in user1 then i can speak only with him. User2 can’t see this conversation.

I don;t have idea how can create this.. I think install bbforum, but this plugin don’t have private topic with one person.. But only in one group..
For help i put beer :).