Send Keyboard Media Keys with Keyboard Library
You have to do some tweaks to the usbkeyboard libraries that comes with the IDE. 

For a video tutorial, take a look at this:

Arduino Leonardo as a multimedia keyboard

Which uses the information from this site, if you prefer text only:

Arduino Leonardo multimedia keys

The Leonardo and ProMicro both use the ATMega32u4 and should both work with theses tweaks. If you need more functionality than the ones that this tweak gives you, you have to dig down into usb descriptors on usb.org for the commands you need.