The services offered at TestFlightApp.com will no longer be available after February 26, 2015. To prepare for the TestFlightapp.com closure, developers and team leaders are recommended to transfer their testers to the all-new TestFlight Beta Testing in iTunes Connect.
Apple acquired TestFlight just under a year ago and has been slowly integrating its features into iTunes Connect.
The transition will be a bit of an inconvenience for developers who already have their apps and testers set up on the original site. In a support document, Apple notes that team leaders and developers can use the Action menu to export tester's contact information into a CSV file. That file can then be imported into iTunes Connect. Click here for detailed instructions.
Any existing apps that were built with the TestFlight SDK will continue to function like normal, but Apple says you should remove the TestFlight SDK from future releases.
More details can be found in the support document linked below...