Unable to install drush on mac 10.9.2
I have encountered the same error while installing the drush on MAC, I have tried the following and that worked for me:

composer self-update
ln -s /path/to/drush/drush /usr/bin/drush


I have downloaded the Drush from this git repository: https://github.com/drush-ops/drush  

And followed the method described here for installing the Drush on MAC: https://www.drupal.org/node/1674222



For Installing Drush on Mac using Homebrew, check https://www.drupal.org/node/954766