Solitaire by Alice Oseman

Sixteen-year-old Victoria "Tori" Spring is the personification of angst, slowly slipping, day by day, into the depths of despair. On a good day, she can convince herself she feels nothing. Her best friend has become preoccupied with boys; her brother, Charlie, is recovering from an episode of mental illness and attempted suicide; a former childhood friend has suddenly resurfaced with expectations that she can't fulfill; and her mother cannot tear herself away from the computer long enough to notice Tori's decline. Then, there's Michael Holden, the crazy new student who refuses to let Tori alienate herself from him the way she is doing with everyone else. He forces himself into her life at the same time as a bizarre prank is unleashed to instigate rebellion among the students at Higgs. Solitaire.co.uk delivers messages via blog posts and by commandeering the schools' computers and PA system, touting a rallying cry of "Patience Kills." Strangely, all of its enigmatic messages seem to bear some resemblance to episodes in Tori's past. When the pranks begin to turn dangerous, Tori convinces herself that she's the only one who can put a stop to it.