Michelle Trachtenberg, right, 13 in this 1999 photo, also got her start on Nickelodeon, guest-starring on &quot;Clarissa Explains It All&quot; at the age of 8 and appearing as a regular on &quot;The Adventures of Pete &amp;amp; Pete&quot; at 9. She played the title role in 1996's &quot;Harriet the Spy&quot; and played Penny opposite Matthew Broderick in 1999's &quot;Inspector Gadget.&quot; At 15, she was cast as Dawn Summers in &quot;Buffy the Vampire Slayer.&quot; Photo: CRAIG T. MATHEW, HO / AP1999