Tokyo stocks plunged sharply by midday Monday, the first trading day of 2014, as investors cashed in on recent gains after the Nikkei index soared late last year. The 225-issue Nikkei Stock Average lost 355.28 points, or 2.18 percent, from Dec. 30 to 15,936.03. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was down 13.45 points, or 1.03 percent, at 1, 288.84. Decliners were led by mining, marine transport and rubber companies.