Alton Sterling, a black father of five, was shot and killed by a white police officer on Tuesday. Philando Castile, a black cafeteria supervisor, was fatally shot in his car on Wednesday. Their deaths are the latest in a string of police violence against black people, and it has to stop. The more voices who support black lives matter while protesting police violence, the faster (hopefully) change will come. Here are the celebrities who reacted to Alton and Philando's deaths on social media, and are using their platform to raise awareness for this crucial issue.