Help! missing sister

So my little sister asked me if she could go outside (she’s 17) so anyways her and her friend were going to talk outside the house and that was almost hours ago, now she’s not responding messages or calls or anything. I don’t know what to do. I told her that she could so I’m responsible for her and I feel so guilty, my mom is sleeping and I just don’t know what to do anymore please what should I do?? I walked into her room and she placed her pillows in a row and covered them with the blanket.. I’m just so scared and worried