Investors pulled a net $23.96 billion from stock mutual funds in December as the stock market fell. December’s outflow was heavier than November’s $2.10 billion. And it was the fifth month in the past seven with outflow. Also, it was the most outflow this year and since December 2012’s $30.63 billion, says the Investment Company Institute. Signs pointed to inflow resuming this month. Funds that invest primarily in the U.S.