Apple has begun sending emails to inform legacy TestFlight users that the service will be closing down on February 26, 2015, following Apple's purchase of TestFlight's parent company close to a year ago.
Apple is moving TestFlightApp.com users to its all-new TestFlight Beta Testing found in iTunes Connect. Apps won't be instantly transferred to the new service, app developers will need to set up their apps for the new TestFlight Beta Testing in iTunes Connect.