I get black flecks on my butter when I grease my pan I recently bought a Teflon-coated pan and have been using it without cause for concern, but while greasing it tonight I found the butter stick I used came away with grey flecks / residue.

I typically handwash it, but I have also used steel wool in the past to get burnt food out quickly. Have I somehow removed the coating? Is it safe to use this pan?
Never use steel wool on teflon-coated pans!!! 

You surely have scratched and damaged the teflon and some of it came off the pan.

I'd throw it away.