Tech giant Meta is partly responsible for the alleged murder of an NYC teen, whose killer relentlessly harassed her online before her death, her devastated dad said in a $50 million lawsuit. The alleged killer, a 15-year-old unsupervised foster kid, launched a month-long cyberbullying campaign against Emery Lynn Mizell, 17, via Meta Platforms-owned Instagram, which has “actively concealed” the dangers of the platform, the victim’s father, Tony Mizell, claimed. The culmination of the harassment came on May 2, 2024 when the 15-year-old girl fatally stabbed her in the chest as she walked home from school in Soundview, according to the Bronx Supreme Court case. “This tragedy was entirely preventable,” Mizell said in court papers, which also blames the city Administration for Children’s Services, which he claims did nothing to discipline the unhinged teen or lift a finger to intervene. Emery was walking home from school in the Bronx when she was stabbed in the chest, allegedly by another teen.…