Solving an "wireless tools not found" error from airmon-ng tool
Unfortunately, airmon-ng is not working on OS X, you will probably have to use a virtual PC with a linux OS + USB WiFi dongle. From FAQ:

Is Mac OS X supported?

The aircrack-ng suite has limited Mac OS X support. Currently it only supports the following tools: aircrack-ng, packetforge-ng, ivstools and makeivs. Any program which requires opening a wireless interface is not supported.