Work isn't always a good time. That's why we've got to celebrate when we can. You may "woohoo" at your own discretion.
Don't formally schedule the celebration with your HR department, but instead, organize a party that allows everyone to let their hair down and be human together. Camaraderie within an organization leads to higher employee morale and ensures that your most valued colleagues stick around.
Don't forget to celebrate the successes of those outside of your own company. Industries are microcosms that inevitably involve a lot of horizontal movement from one company to another. Creating a fun sense of camaraderie where competition is friendly makes passing the torch something that's bittersweet—instead of just bitter.