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Teen Titans seems the most obvious, but that is probably too popular to be forgotten, plus it had 5 teens. Perhaps it could Shaolin Showdown?
You mean Xiaolin Showdown.
Unfortunately, that's not stop-motion.
You might be thinking of Phantom Investigators.
"And it was also animated in stop-motion/claymation.". Neither Teen Titans nor Xiaolin Showdown was stop-motion.
I don't have a guess, just that correction.
Sorry, didn't notice that caveat.
Yes! It WAS Phantom Investigators! Thanks!
I remember that this show was on Kids WB, and appeared on Saturday Mornings. It featured four teens, who I think had superpowers. One MAY have had the ability to transform into creatures....
And it was also animated in stop-motion/claymation.