Apple has dropped native support for PPTP VPN in macOS 10.12 Sierra because the protocol is no longer considered secure.  Note: PPTP has also been removed from iOS 10.

PPTP connections previously setup in the Network system preference pane will be automatically deleted after upgrading to Sierra, and the option for PPTP has been removed when adding new VPN connections.

Several Sierra compatible third party VPN apps are however available that still support the PPTP protocol, including VPN Tracker and Shimo.