Firstly, welcome to the forum
You don't say what Sw you use for processing your RAW images, but Lightroom 5 does a pretty good job of noise reduction (and other, specialist noise reduction packages can do even better).
I would be tempted to shoot some images at higher ISO than you would normally to try and get the shutter speed higher - without seeing images or knowing what settings you've tried it's difficult to give specific advice, but remember that an image that appears noisy when viewed at 100% on screen, might look fine when printed or scaled down for web.
You can also convert to B&W - this doesn't remove the noise directly, but sometimes noise in a B&W shot is considered less of an issue.
Another option (which depends entirely on the stage set, etc.) is to actually embrace the motion blur - IE take a few shots where the stage is sharp, but the performers are 'artistically' blurred as a way of showing the movement. It's one of the big advantages of digital - you can try taking a dozen or so such shots (with varying shutter speeds), and if none work you've lost nothing!