These Bodies Between Us by Sarah Van Name

A wistful coming-of-age story with a haunting twist about four friends who spend their summer learning to become invisible-but disappearing comes at a cost.
Four girls. Four girls skating home, both sides of the road, fearless. Four girls at the mouth of an infinite ocean, sugared and salted with sand and seawater, the tide licking their sunburned feet.
This summer, they're going to disappear.
For seventeen-year-old Callie and her best friends Talia and Cleo, every summer in their small North Carolina beach town is as steady as the tides. But this year, Cleo has invited enigmatic new girl Polly to join them, creating waves in their familiar friendship. And Cleo has an idea, gleaned from private YouTube videos and hidden message boards: they're going to learn how to make themselves invisible.
Callie thinks it's a ridiculous, impossible plan. But the other girls are intoxicated by the thought of disappearing, even temporarily-from bad boyfriends, from overbearing families, from the confusing, uncomfortable reality of having a body altogether. And, miraculously, it works.
Yet as the girls revel in their reckless new freedom, they realize it's getting harder to come back to themselves. and do they even want to?