You can imagine the characters as whoever you want, but this is how I imagine them. (Yes, most of them look way to old for high school. You don't need to remind me).

Lyndsey Fonseca as Ava Grey.

Fransisco Lachowski as Caleb Peterson.

Sean O'pry as Tommy.

River Viiperi as Finn Grey.

Mathew Noszka as Sam Williams.