By Seth Fiegerman, CNN Business

(CNN) -- Google's parent company now has more than 100,000 employees.

Alphabet said Monday that it had 103,549 employees in the first quarter, up from 85,050 employees in the same period a year ago.

The addition of nearly 20,000 employees in the last year highlights the company's expanded ambitions. In recent years, Alphabet has expanded into cloud computing, hardware, self-driving cars and more.

But Alphabet remains an advertising company at its heart. Alphabet posted $36.3 billion in revenue for the first three months of 2019, with about 85% of that coming from Google's advertising business.

However, Alphabet's overall revenue increased by just 17% from the same period a year earlier, missing Wall Street estimates and potentially raising concerns that the company's core business faces growing competitive pressure not just from Facebook, but newer advertising players such as Amazon.

Alphabet's stock fell nearly 7% in after-hours trading Monday following the earnings report.

At its current headcount level, Alphabet has nearly three times as many employees as Facebook. But it is still much smaller than Amazon, which has more than half a million employees — many of whom work in retail and fulfillment roles.

For years, Google was known as one of the top places in the world to work. Its famous perks ranged from complimentary gourmet lunches to office slides — so many slides, in fact, that at least one publication ranked the best of the bunch.

More recently, however, a darker side of its corporate culture has come to light. In November, Google employees around the world staged walkouts to protest what they say is a workplace culture that turned a blind eye toward sexual harassment and discrimination.