Program disappears after shut down

The Team Viewer program seems to disappear everytime I shut down my computer. I am on a Mac Book Pro running OS X El Capitan. Previously it would dissapear if I closed the team viewer program itself but as long as I left it up in the background I could close and shut down my computer and it would still be there when I started my computer back up. I recently had to have my operating system reinstalled and since then every time I close my computer or shut it down the program seems to disappear and I have to reinstall it every time I want to use it. 

Unfortunately I'm not very tech savvy so I'm not sure what to do to keep from having to reinstall it all the time. Any thoughts?