Chat between logged-in users and Admin

Hi guys,

I have been trying to achieve something using a plug-in but unable to. Any help in pointing me towards a relevant would be greatly appriciated.

This is what I am trying to achieve:

I will have registered users and I will have admins. When an user logs-in, I want him to be able to see admins who are online and give her/him the ability to start a chat session/email with an online admin. I don’t want the logged-in user to see any other users who might also be online but are not admins. Only Admins are visible to logged-in users.

Any plugin that would help me achieve this?

Thanks,
Rajiv