The log files on Windows are stored in a common location.
%LOCALAPPDATA%\Plex Media Server\Logs\PMS Plugin Logs\
Using the Finder's "Go" menu, select Go To Folder... then enter the following in the dialog box that pops up:
~/Library/Logs/Plex Media Server/PMS Plugin Logs/
Note: Server versions prior to 0.9.16.0 will have logs located at
~/Library/Logs/PMS Plugin Logs/ instead.
In general, the Plug-Ins folder for the various Linux versions of Plex Media Server will be found under:
$PLEX_HOME/Library/Application Support/Plex Media Server/Logs/PMS Plugin Logs/