If you are not seeing any maps while using TPE, please confirm that your device is connected to the internet in the first instance. You can do this by checking email, or viewing a web page in Mobile Safari.
If you have confirmed that you're online, then try selecting an alternative map type using the map type selection controls. Sometimes, a map may appear to be missing but is in fact simply showing a blank area:
If you still cannot view any maps and if your device is connected to the internet using mobile or cellular data (i.e. not using WiFi), then confirm that you have allowed TPE to us mobile data:
1) Under iOS Settings, choose 'Cellular':
2) Search for the section titled 'Use Cellular Data For:'
3) Confirm that TPE is shown as enabled for Cellular Data: