Connecticut Retirement Plans and Trust Funds, Hartford, will hire an executive search firm to find a new chief investment officer to replace Thomas E. Flanigan, who was fired last month, said Bernard Kavaler, spokesman for the $22 billion system. The states Investment Advisory Council authorized Denise L. Nappier, state treasurer, to do so. Mr. Kavaler said there is no timetable, but he expects a search firm to be hired soon. The council also urged Ms. Nappier to fill critical management positions at the pension fund without waiting until a new CIO is hired, including an investment officer to oversee alternative investments, Mr. Kavaler said. Michael MacDonald, who headed alternatives, left the system in the fall to join Chase Capital Partners.