What Can I Do To Help My Mom with my 16 year old sister? My sister is running the streets like a grown woman.

She's my younger sister and my mom calls me and complains how my sister doesn't come home after school, she stays out late even on school nights and don't call or text. My mom said when my sister do decide to come home she runs straight to the bathroom so she probably out there doing something she has no business doing. Should I step in and say something to my sister? Or stay out of it?