If I buy a Nikon flash, will the autofocus in the dark work?

I have a Nikon D5100 and work in nightclub photography, it is hard to focus and I'm forced to use manual focus. Will getting a Nikon flash enable my autofocus to work? If so, which would you suggest?

You should check with a few nightclubs about this. They may not want flash photography destroying the ambiance. But some may think that it is OK. For those that accept flash photography, I found Nikon flash units prohibitively expensive, so I shopped for a third party flash with excellent ratings. The brand I chose, and still use, is no longer available, so you would have to do your own shopping.

You should avoid a flash in a nightclub. Learn to use the manual focus on your camera, although with no flash your shutter speed is going to be relatively slow which will blur any movement of your subjects or of your camera. Furthermore, your ISO will have to be relatively high, which can cause graininess in your photos. In summary, shooting in a nightclub is very challenging, even for a professional.

Some flashes provide focus assist in low lighting conditions. Make sure the flash you are getting has that feature and is fully TTL compatible with your camera's specific model.

Personally, I find that feature annoying though on both sides of the camera. I'd rather shoot using DOF instead.