How to find who is doing this?

[Bosco]

Not too much you can do on twitter except you can lure him/her to a phishing site. The coding is relatively simple and it costs nothing (PHP) Just have it capture the IP of the person on the site, and send it to you as a message. All you gotta do is tweet to them the shorthand version of the link, and that person will definitely click on it. Another messed up way to go about this is to have a java client running on the site (more advanced coding) and download a RAT (Remote Administrative Tool) to their computer which will allow you to control their computer and figure out who it is. I would go with the IP one because RATs can be deemed illegal. IP cannot be because many many many sites including yahoo store your ip each time you log on, and from there can tell if you switched locations which might mean someone is trying to hack your account.

Give it a try