I am having MAC OS X(Sierra) 10.12.2.
I set ANDROID_HOME to work on React Native(for Android apps) by following the following steps.
Open Terminal (press Command+SpaceBar, type Terminal, Hit ENTER).
Add the following 3 lines to ~/.bash_profile.
export ANDROID_HOME=$HOME/Library/Android/sdk/
export PATH=$PATH:$ANDROID_HOME/tools
export PATH=$PATH:$ANDROID_HOME/platform-tools
Finally execute the below command (or RESTART the system to reflect the changes made).
source ~/.bash_profile
That's it.