OS X Mavericks doesn't recognize my Nexus 5 when plugged in via USB

Not sure if you ever solved this as its 30 days old, but in OS X you need The Android File Transfer App running in the background in order to mount your Android shares. Hope this helps.

I had a similar issue albeit in my case the cause was my usb cable. It was manufactured for power supply and hence let no data through. Switching the cable let me connect my Android device without further problems.

My solution strictly involved replacing the cable. I found the original cable for the Nexus 5 and the problem cleared. Two other cabled failed to activate the program in my macbook air.