The app is in the app store, but I just found this message:
If your company is using Facebook at Work, you can set up your account by clicking the link in the email you've received or by visiting [YourCompanyName].facebook.com from your computer.
Once you've set up your work account, access it on mobile by downloading teh iPhone app from the iTunes App Store or the Android app from the Google Play Store.
//
Le sigh.
