Michelle Trachtenberg Through the Years

Michelle Trachtenberg was one of those cases of "gone too soon" ... and we're marking what would have been her 40th birthday by sharing a gallery of photos from throughout her career.

The performer started off her professional journey when she was just a kid, and her star really shone during her multi-season run on "Buffy the Vampire Slayer."

In February, she was found dead in her New York City apartment, and several of her past costars paid tribute to the late actress.