A sayaad is a devourer of souls, dominator of wills, and tempter of hearts. It knows nothing but evil.
Salacious tales refer to the demon by its common name: succubus for females, incubus for males.
A stimulus is required to beckon the creature. With a symbol of love as bait, it will surely answer your call. Defeat it, and make it your tool.
It will be hard to find a thing of this nature, though. You should speak with Takar the Seer. You will find him in the Barrens of Kalimdor near Camp Taurajo.