Uh... so you gave $100 to some random stranger over the internet? Sorry, how did you give this $100 in advance? Was it in person? Or over the internet? If it was the prior, then that should have been a MASSIVE red flag.
How do you know this kid is a tutor or dux?
Honestly there's not much you can do. If you didn't meet up with this guy, then he could be some person on the other side of the world, or in another state. Only option is to bluff and scare him.
I would first message him and ask you want a refund, before this - try and get as much of his details as you can (since i'm better he'll block you when you ask this). If he declines, then threaten to take him to small claims court.
You probably don't wanna actually take him to court, but hopefully the threat or you saying you are will scare him into refunding the money.