John Dominguez, who last year helped start PrivateTrade, a secondary marketplace for institutional investors in private equity, has left the firm, said Justin Meise, spokesman. Mr. Dominguez previously was director of alternatives at the $32 billion Public Employees Retirement Association of Colorado, Denver. Mr. Dominguez, who was a managing director at PrivateTrade, still owns a minority stake, Mr. Meise said. The firm is searching for a replacement. Mr. Dominguez was not available for comment on his reasons for leaving and his future plans.