First of all, I think you need to understand that most celebrities are probably very accustomed to being praised for their work or talent. I'm not sure that getting on Facebook or a video chat room and saying anything about their performance will impress them to the point of being willing to take some of their time to meet you.
I would guess that a more effective approach might be to tell them about yourself. If you are hoping to become a performer similar to the type of work done by the celebrity, tell him/her what you've done so far and ask for hints or suggestions that would help you develop your career further. If you can share specific instances in which their activities have inspired you or others, or if you are involved in planning an event that would involve activities that you know would appeal to the celebrity's interests, tell them about it.
There are frequent stories about celebrities making opportunities for individuals who are seriously ill or who have suffered tragedies of some sort to have some respite through attendance at a concert, game, or whatever the venue of performance for that celebrity. This allows the celebrity an opportunity to do some good for someone else as well as giving the receiver the thrill of meeting that person. If you can help establish the connection between the celebrity and someone who needs their help, you might be invited to come along for the performance!