Rotating an Object with Touch and drag

I have a scene with a object in it, I want to be able to touch on the screen and when I drag in a direction it rotates the object in place In that same direction. Giving the effect that you can have any normal, off the object, line up with the center of the camera. For example if the object was a person, If I drag down the rotation should make the top of his head facing directly at the camera.