Apple’s messaging feature has long been a source of frustration, with complaints mostly concentrated on its inability to recognize non-Apple devices. With the iPhone 5S, the feature has actually gotten worse, which is actually a surprising development considering how buggy it was in the first place. Aside from vanishing text messages, a number of people have reported that they have been unable to send iMessages.
If you’re an iMessage loyalist, you can restart your phone and hope for the best. If not, we would advise you to cut your losses and just send regular text messages. The answer to your problems can be found at Settings>General>Reset>Reset Network Settings.