It depends on the situation. If you're speaking to a friend, you should use the following:
請問找誰人=Who are you looking for?
請問你們喝什麼?=What do you want to drink?
If you need to show respect to the people, you should use the following:
請問找誰人=May I ask who you're looking for?
請問你們喝什麼?= What would you like to drink? or... Would you like to drink anything?