I've had serious social anxiety all my life. I've gotten a lot better though. Bulking up has helped (my doctor told me that people who are around a normal weight tend to be relaxed mentally, and it also boosts confidence). One thing that I didn't expect to help me socially is Tai Chi. Tai Chi is a really slow motion martial art that makes you feel you're entire body at once and be able to move it as one. I can't explain why (still figuring it out), but this type of movement helps confidence and therefore social interactions.
As far as supps go, I find that Rhodiola works really, really well for me if I take it occasionally (no more than a couple times a week, or you'll build tolerance). You can also combine it with a green tea for a nice boost, as rhodiola boosts the effects of caffeine. You can also take it with red bull if u want to get a little high, but I recommend against that in social situations.
My doctor has prescribed me Ativan for social situations, but I only use it in really large crowds, very sparingly.
One thing I want to make aware for people who have not had to deal with this problem, or at least not to a great extent, that it is a lot more than making yourself confident. You can do that, and remove the reasons of panicking in a social situation, but this is often not enough. Your brain has wired itself to panic for many many years, and just because you remove the reason that doesn't mean the programming automatically goes with it. For me, it takes meditation to close this gap (one way to look at it is computer programming for humans).