Use the Android SDK Tools:
avdmanager
Or you can also start it by using the command below but it's deprecated though on newer version. Before executing it, make sure to export your Android SDK's tools directory in your ~/.bash_profile
(i.e. export PATH="/Users/user/Software/android-sdk-macosx/tools:$PATH"
)
android avd
Old answer:
In order to open the avd manager on terminal, execute the following:
/usr/bin/java -Xmx256M -XstartOnFirstThread \
-Dcom.android.sdkmanager.toolsdir=/path/of/android-sdk-macosx/tools \
-classpath /path/of/android-sdk-macosx/tools/lib/sdkmanager.jar:/path/of/android-sdk-macosx/tools/lib/swtmenubar.jar:/path/of/android-sdk-macosx/tools/lib/x86_64/swt.jar \
com.android.sdkmanager.Main avd