The name and location of the output files is maintained in the site's tracesettings.config file in the listeners section. An example from the server is shown below:
<add fileName=".\TraceLogs\SPFServerTraceRolling.log" header="" footer=""
formatter="Server Format" rollInterval="Day" rollSizeKB="2000" rollFileExistsBehavior="Increment"
listenerDataType="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.RollingFlatFileTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
traceOutputOptions="Callstack"
filter="All"
type="Microsoft.Practices.EnterpriseLibrary.Logging.TraceListeners.RollingFlatFileTraceListener, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
name="Rolling TraceListener"/>
Modify the filename to the path you require. Each log file needs to write to a separate folder to the other web service log files, otherwise the log file may not write.