A gun scare on social media prompted extra security at a Sarasota high school yesterday. The Sarasota County Sheriff’s Office said a student from Riverview High School posted a Snapchat photo of a weapon and used language suggesting he may bring the weapon to school on Wednesday. Authorities questioned the teen at his home, where they found an airsoft gun. The sheriff’s office added extra patrols at Riverview High out of “an abundance of caution.”