If it's not in the folder, look in the original installation set, and reinstall from scratch.
BUT firstly also check that the new computer has FULL permissions set to the Plugins folder - Windows might have prevents some files being auto-installed, you need FULL permissions...
See here... http://sketchucation.com/forums/viewtopic.php?p=508319#p508319
You can also get that .so file from SCF...
http://sketchucation.com/forums/viewtopic.php?p=380121#p380121
Make sure you use the right one.
Since you choose not to share your OS/version with use, please read the notes about usage and which version of the .so is needed for which Ruby etc...