How did you get the paint to stick to the mask?  I have a cyberpunk mask that uses the 3M respirator and the paint always flakes off for me--  which works out a little since I like the weathered and distresses look it gives, but with more control, it could look better.

For smooth plastic surfaces there are a few things you can do to help spray paint stick.  Firstly there's quite a difference between different brands of paint and some work a lot better than others.  I've had good success with Loop, PlastiKote and Hycote

Secondly - sand the surface down with fine-grain sandpaper, fine wire wool or (at a push) one of those rough green dish-scourers.  The effect you're aiming for is a dulling of the plastic's shine rather than serious scratches so be gentle.  This gives the surface a host of micro-abrasions that the paint should adhere to better than a seriously smooth surface.  Make sure to clean the surface of dust afterwards.

Finally, if the above two are not sufficient then also use a primer.  Most spray paint brands have their own primer and it's probably best to match within a brand for best effects.