First of all, I wouldn't recommend feeding live food on a regular basis, and, it should be enriched first of all anyway with something like Dan's Feed from seahorsesource.com.
If it is feeding on pods for sure then I would say you're not in an immediate panic. However, you could get just a few ghost shrimp and see if it is interested in them still. Other than for a trial period I would say always enrich them first.
You can try to feed thawed and rinsed mysis using a baster and putting the food right in front of it's snout, or, you could try a feeding dish with a few pieces in it and see if it responds.
Hatching live newborn brine shrimp won't be any good for a seahorse of any size other than fry or dwarfs because they can't be bothered snicking something so small.
If all else fails you can order live brine from livebrineshrimp.com.
Make sure whenever you put another one in the tank that it comes from the same breeding source as some stores have more than one source.