The only known hormone of sea stars are the gonad-stimulating substance or GSS is a neuropeptide that is released one hour before spawing their young. The neuropeptide is released from the radial nerves where they go to the body cavity. The hormone lets the ovaries form another hormone which induces maturation and spawning for the young.
Female sea stars are the ones commonly studied so not much known on the other hormones of starfish.
A Study In Biology 