How to stop an app from running completely on OS X?
It is probably a launchctl process that is restarting.
To see all loaded launch agents, in Terminal:
launchctl list
To remove one:
sudo launchctl remove label_of_program_to_remove
where, label_of_program_to_remove is found in the preceding list. Note that you have to run the sudo command from an administrator account; or, su to an administrator account first.
Go to the Teamviewer preferences. Under the general tab unclick "Start TeamViewer with system". Apply and afterwards you should be able to close the program.