Running the Android emulator from the command line
To enable running the Android emulator from the command line, you can use the "emulator" tool provided by the Android SDK. This tool can be used to run the emulator from Terminal on OS X or from Command Prompt on a Windows machine.
To launch a specific Android emulator, run the following command from the tools directory in the android SDK location (such as C:\android-sdk-windows\tools);
emulator.exe -avd NameOfYourEmulator -partition-size 512
On OS X;
./emulator -avd NameOfYourEmulator -partition-size 512
The reason for needing the partition size is to allow the emulator to have plenty of space to get the Xamarin.Android platform installed on the emulator as by default the size of the emulator is small.
You can find out more information on extra parameters on the Android site here - http://developer.android.com/guide/developing/tools/emulator.html