The Dow Jones industrial average and Standard & Poor’s 500 index are closing at record highs Monday as investors regain their appetite for riskier stocks.

Twitter was one of the big gainers, rising $1.89, or 5.9 percent, to $33.94. Facebook climbed $2.59, or 4.5 percent, to $59.83. After beating down Internet and small company stocks for two months, investors decided that they had fallen enough.