Hooking up and dating

Nope, nope, liked, nope, liked, liked, nope: This is what romance looks like on Tinder, the fastest-growing mobile dating service in the nation, and either the most superficial one to be invented or the one most honest about the primal instincts that have been drawing strangers to each other since the beginning of time.

Kimbal, a chemistry teacher trying desperately to dodge repeated seduction attempts from his students.

About two-thirds of teens say at least some of their friends have hooked up.

Nearly 40% say they've had sexual intercourse during a hook-up.

"I think young people are getting the message earlier and earlier that this is what everyone is doing," says Stephen Wallace, chairman and CEO of Students Against Destructive Decisions.

Teens also have access to the Internet and text messaging, which impersonalizes relationships and emboldens them to do things they wouldn't dare do in person.