My 12 year old niece is becoming way too sexualized too fast. Her parents don't know but I have access to her social media. HELP!!

My niece doesn't have the best parents. My brother (her dad) tries to buy her love but doesn't actually make an effort to connect with her emotionally and only sees her a few times a month. Her mom has been on and off with her step dad who she tells me has been a good father figure in her life, but it seems like there is still something missing. She started going to a new school for grades 6-8 in the middle of the city and it's been rough ever since. She's been dating these boys who constantly "cheat" on her when they find "hotter" girls to date. When this happens she posts lamenting messages about being heartbroken and she cries at school. Other kids in her class refer to her as a hoe and ask her why she cries at school all the time. These are all huge red flags and I know she needs some affection from someone who cares for her. I've planned to meet her for lunch this week but I just saw her post on Instagram that she just "needs some good dick and a hug" and I don't know where to go from here. I feel pretty lost. What do I say if she's already gone as far as having sex at 12??!! She's a child and is obviously very hurt to be acting this way. What can I do to help? (I'm her aunt and I see her very infrequently as well) via /r/Parenting https://ift.tt/2DWFexT