how do I report this crime?

Well technically (in the US), its not a crime unless they actually have sex or have “sexual contact” if not the most that could happen is indecent relationship with a minor, but she’d have to testify to that and file a report, and I doubt she’d do that if she really likes him. All I can suggest is look at his ID so you know what his age is for sure, and maybe tell her parents. Keep in mind, your friend won’t appreciate your actions and you may very well lose not only her trust, but her friendship

Yea good point, but unless they actually have sex you might not be able to do anything besides tell her parents. Though you may wanna look into what the law says about the age limits when it comes to Americans dating people from other countries, that might be helpful, those laws seem to be more strict. Also, in America its illegal for someone to take a minor over state lines without parental consent, so if hes providing transportation to Michigan for her, that would be kidnapping, even if the minors ok with it, so look into that Good Luck, honestly, most people especially young girls, aren’t brave enough to do risk their friendships like that. Fun Mail me if you want

This is just a random guess but I don’t think it’s legal to go online and lie about your age and talk to minors..? its just a guess though, maybbe you could look into that