I have no experience with Logic, but I'll try to shoot this in the dark. I assume you mean that the Logic plugin does not show up. In this case, it might be in a plugin folder that Logic does not recognize. If Logic has a way to manually add plugin folders, try searching for your Kontakt plugin, and adding that folder so that Logic knows where to find it.
Another possibility: when you installed Kontakt, did you install the Apple AU plugin? Maybe Logic is looking for an AU plugin, but you only have a .vsl or .rtas plugin installed.
Another thing to try: consider re-installing Kontakt, and specifying where to put the AU plugin if it gives you an option (somewhere where you have other AU plugins that do show up, like a default AU folder if there is one). Also, try installing both 64 bit and 32 bit plugins, if you did not.
I realize that these suggestions are very abstract, as I don't know the details of the system. Hopefully someone with logic experience will have some more specific tips. If not, consider trying a Native Instruments forum where they should have a more in depth knowledge of Kontakt. For example: