you can also try moving log4j properties file out of WAR into root of weblogic domain where WAR is deployed. I thought this is a best approach as when ever you do make any changes you dont need re-deploy the WAR but yes you need to bounce the server
To answer you question. I think i also got this issue. Some times when you do'nt mention absolute path, it may create the log files under root drive where domain is running. For eg, if your domain is running under c:\domains\sampleDomain it may create log file under c:\xyzlogs\xyz.log
Check it out and also make sure you have enabled the appender you are refering.
Andy