systemctl: command not found

First you need to check if systemd package is installed – sudo dpkg -l | grep systemd.

If not then install it by hands sudo apt-get install systemd. But if it does it might be damaged, so you may try to reinstall it sudo apt-get install --reinstall systemd.

If the package is installed, even after reinstallation it does not work, list the full path of the files inside this package sudo dpkg -L systemd. Maybe binary files are located in a directory that is not included into $PATH variable