if you are receiving this error that means that you do not have the genymotion app installed on your Mac
you can to download a .DMG file from here and install it by double clicking on it
you can try and run the installed app but it still won't run as it is missing the underlying virtual machine tool
to run genymotion you need virtualBox Guys at genymotion have mentioned their preferred choice as 4.3.12 which you can download from here
Once downloaded you can double click on the .DMG file and then the .pkg (package file) and then follow the normal installation procedure
once you have the virtual box installed then you can run the genymotion app and you will get there was supposed to be an image here
I was posting an image which would have helped you but SO says i need 10 reputation points to post images. then i decided to help you by posting an imgur url and SO says i need 10 reputations to post more than 2 links
kind request to SO either give me more reputation points or make it easy for me to help others
Now you Gennymotion is finally installed just go ahead and create a new virtual device
and once you have created a new virtual device you can access that device from the Gennymotion Android Studio Plugin
Hope this helps