There's a girl I see at work reasonably often that I have a massive crush on. We talk a bit every time she visits, but she works with my boss so I'm not willing to ask her out at work since I don't think I'm allowed to, and I don't have a phone number. However, a coworker is a mutual friend so I want to send her something on facebook. How do I pull this off? My best idea is something simple, like: "Well this isn't my preferred means of talking, but we should go out for coffee this weekend."

Straightforward and to the point. Should it be something else? What's your advice?