Are they still there when you visit the twitter site via a web browser?
First, try these.
Close/Clear the app: With the problem app closed, double tap on the Home button to get the multitask bar. Tap and hold on any icon in the bar until they jiggle, then tap the minus sign on the problem app. This will remove it from RAM and insure a clean start the next time you launch the app.If that does not work:
If that does not work try a restart,
Restart: Hold down the power button until the power off slider appears. Slide it off. When the iPad finishes shutting down, hold down the power button again until the Apple logo appears. Apple recommends you restart the iPad at least once a month.
and then a reset if that does not work.
Reset: Hold down the power and home buttons until the Apple logo appears. The iPad will reboot. This usually takes a bit longer than a restart.
Try deleting and and re-adding your account in Settings Twitter (if you are using the official Twitter app).
If a different app, do the same in the app.
If neither works, make sure you've got the updated version fo the app. If you do, try deleting the app and adding it again.