Nikon concert photography camera - how many megapixels do I need?

For my son's birthday, I'm getting my son a new Nikon camera. He currently has the Nikon D5200. I found a good deal on the Nikon D7000. Would this be a good upgrade camera for the concert photography that he does? His D5200 captures approx 24 megapixels, and the D7000 captures approx 24 megapixels. Will this megapixel difference take away from the quality of his photos? Not sure how important that particular feature is. Any help is appreciated!

Nothing wrong with the camera he's got. If he's not getting good results that's down to user error.

Get him some faster lenses instead (f2.8 or faster).

If his D5200 isn't broken, he doesn't need a new camera, look at lenses or a flashgun instead.

Concert photography is difficult, even when a DSLR is permitted (most simply won't allow them without a Press Pass), but if he can't get the results he wants with his existing camera, throwing money at the problem won't help.

D7000 is 16 mega pixels. D7100 is 24 Mp.
Between 16 and 24 Mp, not much difference unless you crop heavily. You're better off getting him better lenses. Lenses are a good investment if he stays with photography and is something he will appreciate. You can't go wrong with a 70-200mm f/2.8 lens which is handy for concert venues.

D7000 outperforms D5200 in terms of wider autofocus coverage (more points for focus), and larger color sensor (more pixels). Unless your son specifically noticed limitations on D5200 imposed by focus and color, or other traits (in which case other camera choices would come in), a new camera won't help.
Newer accessories would depend on what he already has.
The difference between 24 and 16 megapixels would matter if he
(1) prints large photos, which sometimes concert photographers do (look at the source below for a discussion about printing), or
(2) crops the photos enough (selecting part of the picture to fit into the rest of the space)