Formal:
* Allez les chercher! (This is the most literal translation and works in most situations.)
* Allez-y! (This is a more general encouragement, meaning "Go for it!")
Informal:
* Vas-y! (This is a more casual encouragement, meaning "Go for it!")
* Fonce! (This is a more energetic encouragement, meaning "Go for it!")
* Attaque! (This is a more aggressive encouragement, meaning "Attack!")
The best way to choose the right phrase depends on the situation and your relationship with the person you are talking to.