If I was you, I'd simply ignore them. It'd be tough for you, or any authority to track someone based on just a BTC address, so if you're not related to what they're messaging you about and have nothing to fear then simply blacklist their email addresses and move on. If you'd like to warn the community you could also post in this forum including information about the extortion attempt such as the email you received and email address it came from; you could do so in the
scam accusation board.
Bitcoin addresses aren't tied to real names and transactions are irreversible, you'd probably have more luck trying to track that person down through the email you received but if he's taking some basic precautions that would still be hard even for authorities. Sorry if you were introduced to bitcoin this way!
