Does this plasmoid work for any of you?
I don't remember it ever working in 4.7 and 4.8, but maybe i'm missing something.

btw, i have nepomuk running and search works when done through dolphin.

To which plasmoid are you referring to? I'm not aware of any being shipped by KDE with that functionality.

It is called "Search Box"
Description: Search Box for a given RunnerManager
Version: 0.1
Author: Artur Souza

I also have the search plasmoid by Souza which when used switches me from my desktop activity to my search & launch activity , obviously it does not work for me. No idea where it comes from

If your interest is in Nepomuk searches then there is a runner available in Krunner

I wonder why this plasmoid is shipped with KDE if it obviously doesn't work. So many good ones are left out.

Which good ones would you be referring to? Note that it is up to applet authors to propose their applets for inclusion within KDE.