What style are you playing? If you're playing heavily distorted stuff, just lifting your finger is often enough. Allan Holdsworth completely saturates his tone for legato playing, so you're able to hear a pulloff when he just lifts his finger. If you're playing with less distortion, though, you'll probably need to actually pull the string in a method more similar to your friends to be heard. If you are playing with a clean tone and you just lift your finger, the pulloff may not sound, at least not as loud as the initial note.