The cause of death for actress Michelle Trachtenberg has been ruled “undetermined” by the New York City Medical Examiner, according to an agency spokesperson.

Trachtenberg's co-stars in "Gossip Girl" shared similar sentiments. Blake Lively, who played Serena van der Woodsen in the series, wrote in an Instagram story that Trachtenberg "w

News of Michelle Trachtenberg's death prompted tributes from her friends and former "Buffy," "Harriet the Spy," and "Gossip Girl" costars.