By Lesley Donelan, Janelle Gonzalez, Samantha Guff, Christina Manduley, Jacque Smith and Madeleine Stix, CNN
They lost their friends and classmates. Their geography teacher. Their coaches. Seventeen people who once shared the halls of Marjory Stoneman Douglas High School with them are gone after one of the biggest mass shootings in US history. And these teens want to make sure it never happens again.