Where the Android-SDK is installed depends on how you installed it. If you downloaded the SDK through their website and then dragged/dropped the Application to your Applications folder, it's most likely in /Applications/ADT/sdk (as it is in your case).
If you installed it using Homebrew (brew install android-sdk), then it's located here:
/usr/local/Cellar/android-sdk/24.3.3 # Don't forget to check your SDK version.
Open the terminal window and enter the following (changing out the path to the SDK to be however you installed it):
export ANDROID_HOME=/Applications/ADT/sdk # or export ANDROID_HOME=/usr/local/Cellar/android-sdk/24.3.3
Once you have this set, you need to add this to the PATH environment variable
export PATH=$PATH:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools
http://stackoverflow.com/questions/19986214/setting-android-home-enviromental-variable-on-mac-os-x