In this case (and others) it has been predominantly Asian gangs who see young white girls as 'trash' and therefore 'fair game'. I'm guessing, but I think they use the racism element as a shield to protect themselves from scrutiny and the authorities play right into their hands by not effectively challenging them for fear of reprisals. Maybe their is also a cultural element to it, but if these gangs were singling out white girls for abuse then THEY are the ones being racist.
Regardless of their race or ethnic background it boils down to one simple fact: they are criminals who are exploiting and abusing vulnerable members of society. No different to anyone else doing the same thing.