Friend advise please help me.?

okay ill tell u the hole story i have a friend named amy and i love her to death! I don't know how long we have been friends.Any ways she has changed ever since we have started seventh grade.Like she wears tons of eyeliner now and she acts wierd around guys and well she acts kinda sluty now..and for christmas her grandma got her a cell phone and she's on it like at all hours of the day but thats not my problem though...i asket to look at her cell phone and she said yes,i excpect forgetting what was on her cell phone.I asket to look at it because i was kind of suspeciuos so i just told her i was playing a game but really i was looking at her messages and pictures.And guess what i found! I she had been texting her frinend that is a guy that she meet on myspace of all places...so i wasent surprised to see messages from him and such but then i looket at it more and there were like things like*rubs ur crotch,then licks*on it from that guy she met so i got kind of embaressed...anyways there was way more like that so i stopet because i was getting sick.So i looket at her pictures and there was pictures of me and her from camp and some other people from our homeroom,but then the next picture was all black so i looket at the next one and she was in her underwear with her hands down her pants and it said at the bottom sent to well that one myspace guy..well it had his name but i dont want to say it.i havent told anyone because i knew that she would get embaressed and stuff,and i still havent to this day and that was like 2 months ago,and then i texted her if she wanted to go to the park to hang out and she said yes so i went,and when i got there she was already there with my friend kelsey so we played basket ball but amy dident because she hates it so anyways the day before she was sitting on a 17 year olds lap at church,really not that bad but wait till i tell u how old she is.okay so she said that the guy she was sitting on was going to drive by and so me and kelsey looket at each other with a ''omg whats gonna happen look'' and so the guy really did end up coming down to the park and he honked and honked so amy finally walket up there and he was drunk and she hugged him and he touched her on her chest so thats really it so srry this is so long but im really scraed for amy what should i do should i tell her aunt or talk to her i dont know what to do please help me