You shouldn't be keeping 4. They will usually fight til the death. Clowns should be kept alone, or in pairs. They are not group animals.
What kind of clowns did you get? Did you buy really small ones? Sometimes if you buy really small ones, getting them to eat can be a challenge. They are best left at the store until they are larger, in that case.
If I were you, I'd try a variety of frozen foods. You can find several types of frozen foods at Petsmart or Petco. Try mysis shrimp, Marine Cuisine Emerald Entree. If you added them recently, it can take several days for them to start eating.
Also, what is your water quality like? Do they have enough rock for hiding places? If your tank is very new or if your water quality is poor, they will be so stressed that they won't eat.
Do you have enough water movement? In a 55 gallon tank, you should have several powerheads. Not enough water movement will stress them too.