'Everyone is going to the party. You should go too.' This inference commits which fallacy?

The appeal rests only on the fact that everyone is doing it.

Popularity and numbers are offered as the reason you too should act.

But wide acceptance of a claim or act does not make it correct or advisable.

Treating 'many people do X' as grounds for 'you should do X' is the bandwagon move.

This is the appeal to the people, argumentum ad populum.