You can find your plugins at the following locations:
OSX
AU: [user]/Macintosh HD/Library/Audio/Plug-Ins/Components
VST: [user]/Macintosh HD/Library/Audio/Plug-Ins/VST
AAX: [user]/Macintosh HD/Library/Application Support/Avid/Audio/Plug-Ins/
WIN
VST: (specified by user at time of installation)**
By Default:
C:\program files\steinberg\vstplugins
C:\Program Files\Common Files\Digidesign\DAE\Plug-Ins
C:\Program Files\FAW\Circle2