Usually when you are on the web site you can just click Help. You may have to pick a topic but then it asks you if their suggestion helped. If you answer "No", then it will let you write them a message.

Also, Kachi posted this to the tech forum at one time. I don't know if it still works:

Kachi: "On the Yahoo! main page, scroll to the very bottom. Click on COMPANY INFO at the VERY bottom. It'll take you to another page, and on that page, you click ADRESSES on the right. It's only the phone # though... and the help there is no help at all. But you can email this address and ask whatever you need to ask (it's not the regular Yahoo! Cust. Serv.): reportabuse@Yahoo-inc.com. Hope this helps someone out there."

HOpe that helps
Kitty