I think my Brother in Law is lusting for someone at 13 years of age.?

Okay, my Brother in law has met this girl online. He met her on facebook. She lives in a different country. He has never met her; but he is already falling for this girl. When I saw pictures of her she looks like she is 13. Well, my Brother in Law is in his mid 30's. He claims the girl is older. But I keep telling him don't believe strangers over the internet. Another reason I am starting to think he lust after 13 year old looking girls. Is because this girl has pictures of herself at the arcade. Yeah, normal adults don't hang at the arcade I tell him. Then, my brother in law makes sexual comments on her pictures of her at the arcade. This is so sick. Words just cannot explain this. Not only that, he is planning on spending money to fly to vietnam to see this girl. He is over his head and thinking in the wrong way. I have talked to him about this and he will not listen. What would you think or do.