Is this sentence proper English?

Well, proper English would mean "faces" should be used, as you're speaking of more than one face. However, you're writing poetry and in my experience, anything goes when it comes to poetry! Even Beyonce's new song, "Who Rule The World" is improper English, unless it's intended to mean girls rule the world. But still, the question should still be "who rules the worl?" Hope this helps. Go out and express yourself however you feel so inspired! It's called artistic freedom.