After you closed GUI of XAMPP Control Panel first time, you can not find the launcher icon again. You have to do following things to make it visible.
1. First you need to install gksu. Type this command on the terminal.
sudo apt-get install gksu
2. Then run text editor like gedit, and type the following. You can copy it from here.
Comment[en_US]=Start XAMPP Control Panel
Comment=Start XAMPP Control Panel
3. Save this file as Xampp.desktop in your Desktop.
4. Once the shortcut is on the Desktop, right-click on it, go to Properties, Permissions tab, and check 'Allow executing file as program'.
Job Done! Now search for XAMPP in Ubuntu search. You will find it now! If you want, you can add it to the launcher also.
Have fun with XAMPP!