Use your experience. Don't want to. Then use the experience you wish you'd had...or hadn't had. Dig deeper into an old friend's prom experience and mix it up a bit. Draw from it and build on it. It doesn't have to be sweet sixteen and blowing out the candles. It can be out of the ordinary. Different.
Prom can be a plethora of misgivings, mishaps, and mistakes, or pleasures, pretty prose, and proposals. If appropriate to your story, don't be afraid to use it or other typical high school events to draw more from your characters and your story. Add a new spin or twist to the prom. You can do anything. Now go write it!