I heard that in the beginning the Dateline series used a decoy pretending to be a 14 YO boy. They have changed to girls because the number of men trolling for the boys looked bad for the MSM favored "minority."
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They've used both "boys" and "girls" at various times -- sometimes in the same series. I do recall reading or hearing something though that said the majority of the perps they are trying to catch seem to target girls. I'll have to do some digging to see if I can find it.