EDIT
Just got a new car and ran into the same problem.
Following these steps: http://visualgdb.com/KB/usbdebug-manual/ as suggested by Veverke in the comment below, fixed the problem for me.
had the same problem and fixed it with a combination of these two links. Obviously, our problem is not the same problem that is indicated in the first link, but why I had to use both options to synthesize the solution.
http://krumelur.me/2014/01/30/xamarins-visual-studio-plugin-missing-android-devices-genymotion-and-parallels-desktop-dont-panic/
http://developer.android.com/tools/extras/oem-usb.html
Basically, in Visual Studio 2013, launch the Android SDK Manager. Scroll all the way to the "Advanced" folder, where you will find the "USB driver for Google." Mine is already installed, so I uninstalled the package, confirmed that I want to remove it, and then reinstalled it.
Then I opened Windows Explorer and right-click “Computer”, then click “Management” (you must specify administrator rights). In the newly opened Computer Management window, I clicked Device Manager under Computer Management> Utilities in the hierarchy on the left.
In the main window, I expanded “Other devices” and saw the device I was looking for. I right-clicked and selected “Update drivers,” then “Browse my computer for driver software.”
Now you need to click Browse... and find where you installed the packages .. for yourself it was C:\Users\zumberge\AppData\Local\Android\android-sdk\extras\google\usb_driver . Click "Next", you need to decide whether to accept Google, Inc. as a reliable source. Then the process should be completed and you will be well off.
I don’t know if VS2013 needs to be rebooted, but I did it for a good measure.
Hope this helps, and it's not too late.