John J. Moon joined private equity firm Riverstone Holdings as a managing director, said spokesman Alexander Gordon. It is a new position. Mr. Moon will be on the investment committee of Riverstones $3.8 billion Global Energy and Power Fund III and $685 million Renewable Energy Infrastructure I. He was managing director at Metalmark Capital, which manages the Metalmark Capital private equity funds and subadvises the Morgan Stanley Capital Partners funds. Vanessa Adler, vice president of Metalmark Capital, did not return calls seeking information on a replacement.