pics will help. i just feed my starfish brine and bits of seafood. theyre happy enough. they still forage but that fine. they clean up an bits of uneaten food my fish miss.
i do the same for my urchin. but i tend to spot feed that though. it has more feet than my stars (all over it, between the spines) so it will grab hold of anything that lands on it, and will pass it down to its mouth.
i dont think they have to be quick to catch live foods though. my urchin ate most of the shrimp in the tank at the LFS, and it sucked one of my hermits out of its shell and ate that. i think starfish could easily do the same if they wanted. but dead foods would be your best bet.