Besides, the simple answer is you cannot. The only people that would know the persons IP address is their ISP and Yahoo, The only IP address your ISP would be aware of is that of the Yahoo Chat server and even you can find that out.
The information on Computing.Net is the opinions of its users. Such
opinions may not be accurate and they are to be used at your own risk.
Computing.Net cannot verify the validity of the statements made on this
site. Computing.Net and Compnet Ventures, LLC hereby disclaim all responsibility
and liability for the content of Computing.Net and its accuracy.