1) did you bleed the brakes?
2) ad it been the booster, the pedal would be HARD. (on the other hand if master & booster are gone, pedal will go to the floor).
3) if you press on the brakes and the engine revs-up, it's vacuum/booster related. Check for leeks on hoses from manifold to booster and see if master's bolts are tight.
4) your master is gone....
You will probably get more info from Peter soon!