Clowns will eat a variety of prepared and frozen foods.
Depending on the size of the fish you could look in the freezer section of your LFS and get a packet of the small cubes.
Mysis shrimp or cyclopeez should initiate a feeding response.
If that is the only fish you will want to cut them into smaller cubes.
It is a good idea to have this in their diet so you can give them more variety.
Also, a thread like this should start in the Beginners section so it will get the appropriate traffic.
Get the small pellets. Crush them btwn 2 teaspoons. And pour it in. Turn off all flow and see if he eats those.
Also grab some crushed flakes. And cyclops.
Mine is tiny too. She eats all of the above if the food is too big she doesn't even look at it.