I think that "元気？" is suitable for "how are you?" in a casual way, but actually the meaning of "元気ですか？" is more similar to asking a body condition, like a "Are you in good shape, or not?", so "最近どう？" or "調子どう？" is more similar to "how are you?".

元気ですか？("Genkidesuka?" - formal, al hablarle a una persona mayor o que ves por primera vez) 元気？("Genki?" - informal, al hablarle a una persona de tu misma o menos edad o por confianza)