One of Us is Next by Karen M. McManus
The Bayview Four were cleared of responsibility for Simon's death, but the void left from Simon's gossip app has spawned copycats. It's then that a truth or dare game emerges with real-life consequences. But someone is pulling the strings, the dares grow deadly, and the attacks are strangely personal, as though that person is out for revenge.
Review from School Library Journal:
The latest texting game, "Truth or Dare," causes a stir at Bayview, a high school in a yuppie California community still reeling from a tragic death linked to a gossip app a year ago. Refusals to accept the unknown texter's "Dare" result in devastating secrets being revealed to the entire student body via text. This suspenseful, romance-filled sequel is told from the perspectives of secondary characters from One of Us Is Lying. Each is facing personal trauma: for Maeve, a potential leukemia relapse; Phoebe, the lingering grief of her father's death and the horror that the school knows she slept with her sister's ex; and Knox, the tension of death threats against a lawyer he volunteers for, and the shame of an unsuccessful sexual encounter that is broadcast to the school. The book opens with a "Contact List" of characters, while reporter interviews and texts from a Reddit forum are interspersed menacingly throughout. Themes of bullying, sexual shaming, and the legal system are highlighted as multiple and seemingly unrelated mysteries unfold, coming together in an unexpected way. Passing references to skin and hair color, cultural and ethnic family backgrounds, a local college athlete who is gay, and the local restaurant's menu of South American foods provide a surface-level, forced sense of diversity to the plot.