Sims Online had a big cybersex brothel problem* for... well, always. Since you can convert virtual currencies into "real" currencies, they had a situation where presumably underage players were literally being paid for their services, through their (EA's) service. The girl leading the ring, which grew into a pretty weird organized crime thing, was 14. I'm not finding the paper I'm looking for right now, but I think it was by Peter Ludlow if interested. If she'd chosen to cash out before the game economy crashed, she would have been an extremely well paid lady.
* A problem for their media image. Presumably added an element of stickiness to the game that wasn't too bad on the bottom line. Also, a pun!
After a bit of searching, I found this link...both interesting and disturbing at the same time. Turns out that the "girl" that led the ring was actually an adolescent male:
* A problem for their media image. Presumably added an element of stickiness to the game that wasn't too bad on the bottom line. Also, a pun!