I don't think tracing and copying, even vectoring, is acceptable in the art community or anywhere else for that matter.

Using another person's piece as a reference is one thing, but tracing it is quite another.
Even being 'inspired; by another piece of work is common among professional artists (particularly in the graphic design community), but copying, and/or tracing is plagiarism.

As for finding a reference, the point of a reference is to get an idea of the perspective and proper proportions, not to copy the actual pose. Don't worry if you don't get it right right away, you're not supposed to. The point is to work up until you don't need references to draw any more. I used a ball-jointed doll for this, as well as awkward snapshots of my friends taken at odd moments, but never the exact picture taken, even if it is mine.

As a kid, I never copied/traced art, and I never have to this day. Even as a kid I knew it was wrong, becuase it's stealing a thought from a person, and I always hated it when other kids did it, because it meant they weren't putting any real work or originality into it.