Ravenclaw: It depends, are these movie-based questions?
If it is, Cho Chang was shunned. (Harry and the whole DA believed Cho betrayed them, but she was forced by Veritaserum).
However, in the books it was Marietta Edgecombe. (She intentionally betrayed the DA by telling Umbridge about it. In result, SNEAK was written across her face (it was the work of Hermione). Therefore, she refused to talk any further, but it was too late. Still, Harry did blame Cho as well, as he thought that she could've better selected her friends).