Is seeking the help of the Prophets, Awliya' (pious people) and good people when they are alive and after their death to lift a person's affliction, bring good and making Tawassul (supplicating to Allah through a means) by them either to fulfill a need or achieve their goals permissible or not?
As for seeking help of the dead, whether prophets or others, it is not permissible, rather it is an act of Al-Shirk-ul-Akbar (major form of associating others in worship with Allah). As for seeking the help of living people with whatever they can do, there is no harm in it, as Allah (Glorified be He) says in the story of Musa (Moses, peace be upon him):
The man of his (own) party asked him for help against his foe
But making Tawassul through living (Part No. 1; Page No. 107) or dead people whether they are prophets or others or through people's honor or rights, is not permissible, rather it is a Bid`ah (innovation in religion) and a means that leads to Shirk (associating others with Allah in His Divinity or worship).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.