SOLID QUARTER: Facebook delivered fourth-quarter results above Wall Street's expectations on Wednesday and sought to show that it has finally transformed into a "mobile company." It generated 23 percent of advertising revenue from mobile, up from 14 percent in the third quarter.

INVESTMENTS UP: Expenses, excluding employee stock compensation, soared 67 percent from the previous year to $849 million, mainly due to hiring and infrastructure costs. It expects expenses, excluding stock compensation costs, to grow by about 50 percent in 2013.

SHARES DOWN: Its stock fell as investors placed more significance on the growing expenses than on its increasing user base and higher advertising revenue.