NEW YORK — LinkedIn posted a loss for the third quarter on Tuesday, but the results were stronger than expected as the professional networking service boosted its user base and increased its revenue.

Such results have become routine for the company. LinkedIn has surpassed Wall Street’s expectations in all of its quarters as a publicly traded company and this one was no exception. But its outlook was below estimates and its shares fell in extended trading. LinkedIn booked a loss of $3.4 million, or 3 cents per share, in the July-September period.