That's a tough one to answer. They always worshiped their gods in one fashion or another, though the names and importance of individuals changed over time. Since the names of the gods relate to what they did, it can be assumed that the prehistoric Greeks worshiped nature.
The main religion worshiping Greek Gods is called Hellenic. Though many New Age Pagans also worship them.
it isn't really similar b/c greek worshipped "pretend gods" while christians worship a one true God.
Research "Hellenic Polytheistic Reconstructionism" to find a local group. Also, ask yourself why you wish to worship Greek gods and what you expect to gain from the exchange.
Prophet Muhammad (S), before receiving revelation, used to meditate to God in the Cave of Hira, and didn't worship the idols that the Pagans were worshiping as gods.
Achilles beliefs were of the Greek gods
in temples
The Olympics were created to worship the Greek gods.
They were polytheistic, meaning worshiping many gods and goddesses.
Worshiping Nyx is not considered Witchcraft alone. You are simply worshiping Nyx. If you wish to practice witchcraft research it before aligning yourself with any deities (i.e. Gods/Goddesses). Witchcraft is not particularly a religion and therefore the worship of Gods and Goddesses is not a rule/must, but many Witches do honor their deities.
No there are not. Greek Gods are treated as mythology these days and not seen as something to worship to.
Egyptians worshipped their own gods, Egyptian gods.They weren't Greek, but their gods were similar
Romans worship their gods through feasting. For example, Saturnalia.....