This article has some interesting theoretical discussion about synthesizing string sounds! http://www.soundonsound.com/sos/Aug01/articles/synthsecrets28.asp
Of course you aren't going after the plucking of a real acoustic guitar but there are some rules of thumb in there that may help you distinguish your sound as more of a pluck and less of a blip that may share a similar ADSR envelope.
One thing I believe helps is harmonics. A simple modeled string being plucked near the center will produce mostly odd number intervals in the overtone series - that is, the fundamental, three times the fundamental, five times the fundamental, etc. If you start off with sine waves weighted at these intervals, then experiment with different waveforms and noise to add bite and color, you are pretty much guaranteed to get a "plucky" sound.
All that said, I like Ableton's "Tension" modeling instrument for this purpose.