How to stir fry frozen veggies?
The trick is to not use a wok at all. A wok works by concentrating a lot of heat on the bottom, more heat than you can achieve with a home stove. "Stir frying" moves the food from the cool sides of the wok, through the intense heat at the bottom, then out.

Rather, use a wide skillet. A home stove can't generate the intense, focused heat of a restaurant stove, but it can generate a lot of heat over a wider area. Put your skillet on the burner, add some oil, get it good and hot, then add your vegetables. The intense heat will defrost them and cook them quickly.

You have to work in smallish batches, probably no more than half a bag. And if you want to stir-fry meat with the vegetables, you may need to temporarily transfer the one out to make room for the other.

As for defrosting... the idea is that you don't need to: thinly sliced vegetables will quickly go from frozen to thawed to cooked when given direct access to very hot oil, and all surface moisture will quickly evaporate. Defrosting them will just give them time to get mushy. 

I'll be honest, I'm not entirely convinced that that's better than defrosting them and allowing the water to drain. But I have observed that when these vegetables come out of the bag, they look nice and clear and perky, and when they're defrosted they look kinda sad. So, maybe there's something to it.

Anyway, that's my advice: use a wide pan, over high heat, with a fair bit of oil, and work in small batches.