#BlackLivesMatter. On July 13, 2013, the hashtag #BlackLivesMatter first appeared, causing a stir. Agitation. Alicia Garza, an angry and saddened California resident, posted a message on Facebook on July 13, 2013, after George Zimmerman, a Florida man who killed black teen Martin, was acquitted. His post included the phrase “Black lives matter”, which soon became a rallying cry.