Shares of Brazil's Gerdau SA plunged the most in almost four months on Tuesday after the Americas' largest steelmaking group announced plans to spend 1.986 billion reais buying out a number of units as part of a broad reorganization program. Under the plan, Gerdau will buy the remaining stakes it does not yet own in Gerdau Acos Longos SA, Gerdau Acominas SA, Gerdau Acos Especiais SA and Gerdau America Latina Participacoes SA.