> one of the addresses set up is a yahoo account is there any way of tracking down who is sending them
So for example they might set up a fake Yahoo account like "
[email protected]", then send an email pretending it was from you.
You can't track that via technical means without the involvement of the police and/or Yahoo. But there are other ways.
Look for example at the style of writing, spelling mistakes, use of punctuation and capitals etc. Compare it to emails from known members, and one or two may stand out.