I'm taking at face value your statement that you're sure you didn't install TeamViewer yourself. If you did install it and forgot about it, then all this is a waste of time.
The only way you can be sure that the computer is not compromised is to erase at least the startup volume and restore it to something like the state it was in before the attack. By "attack" I mean that some unknown person tampered with the computer in an unknown way. The easiest approach is to recover the entire system from a backup that predates the attack. Obviously, that's only practical if you know when the attack took place, and it was recent, and you have such a backup. You will lose all changes to data, such as email, that were made after the time of the snapshot. Some of those changes can be restored from a later backup.
If you don't know when the attack happened, or if it was too long ago for a complete rollback to be practical, then you should erase and install OS X. If you don't already have at least two complete, independent backups of all data, then you must make them first. One backup is not enough to be safe.
When you restart after the installation, you'll be prompted to go through the initial setup process for a new computer. That’s when you transfer the data from a backup in Setup Assistant.
Select only users in the Setup Assistant dialog—not Applications, Other files and folders, or Computer & Network Settings. Don't transfer the Guest account, if it was enabled.
Reinstall third-party software from original media or fresh downloads—not from a backup, which could be contaminated.
Unless you were the target of an improbably sophisticated attack, this procedure will leave you with a clean system. If you have reason to think that you were the target of a sophisticated attack, then you need expert help.
The above being done, change all Internet passwords and check all financial accounts for unauthorized transactions. Do this after the system has been secured, not before.
