1. If you fail to retrieve your stolen gem, you will automatically show up in the Retrieve Logs of your friends and guildmates and they will be able to steal back your gem.

2. Tap the "Request Help" button next to the stolen gem in the Defense Logs to ask help from your friends via Facebook. The game will send a notification to your friends. They should then open the game, find you in the Retrieve Logs and tap "Retrieve".

3. You can always ask for help right in the guild chat.