It's not all that difficult to sort these out. I have emphasized in juvenile offenses for most of my career and kids do not tend to cover their trails well - and they rarely act in a vacuum (i.e. their friends know about it, the details are on social media, phones, and computers, etc.). If the 16-year-old lad is encouraging the child to run away or assisting her, there will almost certainly be a trail. The question is whether or not anyone will take the time to look for it. It all depends on the details. But, when you have a child under 13 that may be being lured away by a 16 year old for what may well be assumed illicit purposes, I suspect they will look pretty hard at it.