I just bought and downloaded The Crew game online to my ps4, and I am wondering why the button of creating a new game is not activated. Do I have to consider buying ps4 online voucher to play the game? or is playable offline?
The Crew is an always-online game.
According to Ubisoft (the game makers):
Players with Xbox Live Silver or PlayStation Network accounts can play The Crew, enjoy Free Ride across the US map, play every mission and skills challenge, cross other players' paths, and participate in all the asynchronous activities that The Crew offers.
However, in order to communicate with others and to dive further into the multiplayer experience with Co-op and PvP, either a Xbox Live Gold or PS+ membership will be required.
It looks like you should be able to play so long as you're connected to the internet on your console. Playstation Plus should not be needed.