Perhaps, being that you are shy, you may not be demonstrating the kind of body language that would make these guys who find you attractive feel comfortable or confident enough to approach you or ask you out.
For future reference, you could look into making positive changes in your body language and see if that makes a difference.
Having your best friend or the mutual friend talk to him will probably only make him feel that much more uncomfortable or intimidated to talk to you.
He may feel like the pressure is on and that expectations are now at a heightened state.
Your better option at the moment may be to use the group of friends strategy and hope that he ultimately gets comfortable enough within the group to start talking to you.
The different time tables will be a challenge but you may not need that many interactions between both groups to have the desired effect of getting him comfortable enough to talk to you.