I already tried this steps:
The error 'require': cannot load such file indicates that you some missing or broken gem package. You can probably fix it by re-installing cocoapods:
gem uninstall cocoapods # Follow by sudo if necessary
gem install cocoapods --verbose # Follow by sudo if necessary
And make sure that your xcodeproj is present:
gem install xcodeproj --verbose # Follow by sudo if necessary
If won't help, try to install it by using older Ruby:
sudo ln -s /Library/Ruby/Gems/1.8/gems/rubygems-update-1.8.12/bin/gem /usr/bin/gem18
sudo gem18 install cocoapods
See: