I got a call from this number saying he's a detective  in South Carolina. But then he said he's in my city. And I know it's from the same number from before. 803413 or something like that. Because I remember his voice. It was that black guy and this time he's claiming he's the girls father. AND he also got the age wrong this time. And it's only been a month. I talked to three different people. 2 claiming to be detectives. There was detective strickland and someone else. I forget his name. All he kept saying was son you're going to jail. And then the detective texted me from the fathers phone. So that's what I knew for sure "hopefully" that it's a scam.

Under Age Girl Scam

Yes it is an extortion scam being run on or by that site.  There are numerous number threads her with the same story.  Make a police report.

http://www.avvo.com/legal-answers/chatting-wi ... pof-887602.html
http://www.thedailyscam.com/underage-girl-sext-scam/
43 pages here:  http://800notes.com/Phone.aspx/1-803-413-4219
http://www.scamcallfighters.com/scam-call-843 ... tics-24322.html

Where should I go to file one and what should I say?

Tell them the whole story.  Your local PD and you should also make a complaint with the South Carolina PD.  You are the victim of an attempted extortion.  They count on people being too afraid to file a report.  The more reports they get the better the chances that these scum will be caught.  They are also branching out to other sites as well.