Facebook is outgrowing its hometown. Where will it go next?

Fourteen years after it was founded in a Harvard dorm room, Facebook is outgrowing its Menlo Park hometown.

And Menlo Park isn’t sad to see Mark Zuckerberg’s social networkers go elsewhere.

Over the past year, the company has opened offices and hired at a blistering pace, with enormous new leases in Sunnyvale, Mountain View and Fremont. This month, Facebook leased all the office space in San Francisco’s new 43-story Park Tower, vaulting it into the ranks of the largest tech tenants in San Francisco. Instagram, a major Facebook subsidiary, recently moved 200 employees into another San Francisco office tower.

“It doesn’t make me panic. It doesn’t make me happy either,” Ray Mueller, Menlo Park’s mayor pro tem, said of the Facebook diaspora. His priority, he said, is a “balanced, financially sustainable” city and improved quality of life for residents.

With more than 10,000 employees in Menlo Park, its headquarters since 2011, Facebook remains the city’s largest employer. And it hopes to grow substantially there, too: Plans for a development on the eastern side of town called Willow Village would allow it to reach 35,000 employees in the city — roughly the size of Menlo Park’s current population.

But the plans, which also include 1,500 rental housing units, shops and 8 acres of public open space, are caught up in a debate over whether Menlo Park has the infrastructure to deal with the impact, including the need for far more housing. And, of course, the big question is how much Facebook would pay.

“As most of you know, I am not squeamish about development, but I am squeamish about traffic,” a former Menlo Park mayor, Mickie Winkler, said at a City Council meeting this spring. Winkler, who was mayor in 2005, not long after Zuckerberg moved his company from Massachusetts to Palo Alto, wants Facebook to produce “an integrated traffic plan for traffic relief.”

It’s a familiar complaint in the region, where the staggering growth of the technology companies, including giant firms such as Facebook, Apple and Google, is putting pressure on housing and — because the paucity of homes condemns workers to long commutes — traffic.

And so, tech companies such as Facebook that once sought to keep workers under one remote roof have had an epiphany: It makes sense to put offices close to where employees live.

“We are interested in offices that minimize commute times as much as possible for our growing workforce,” Facebook spokesman Anthony Harrison said in an email.

When Facebook established its worldwide headquarters in Menlo Park seven years ago, it was near where many of its then-2,000 employees lived, in neighboring Palo Alto. In 2015, Facebook upped the ante with a green-roofed, Frank Gehry-designed building touted by the company as the largest open-floor office in the world.

The idea of such mega-offices is that it’s much easier to forge a corporate culture, because executives and employees are in the same space, said Charles King, president of information technology industry analysis firm Pund-IT.

But that has meant many Facebook employees must drive or take long, tiring shuttle bus rides to work. Some might prefer to live in Menlo Park, but the median price for homes there is $2.7 million, according to Zillow, a real estate website. As Facebook’s global workforce has ballooned to more than 25,000, the company’s voracious real estate appetite must be satisfied. The recent scandal over data privacy hasn’t slowed down hiring. If anything, the company’s push to hire more people to review and take down posts has accelerated it.

Bringing offices closer to where employees live should help reduce traffic, said Matt Regan, senior vice president of public policy for the Bay Area Council, a public policy advocacy group that represents business groups.

Instagram, which was a small San Francisco startup when Facebook bought it and moved it to Menlo Park in 2012, returned to the city this month, to some staffers’ excitement. “Week 1 at the SF office,” Christine Choi, a product designer, wrote beneath a photo of a co-worker in the new space. The Instagram post was punctuated by a smiley face emoji with hearts in its eyes.

Though Menlo Park will remain Instagram’s headquarters, opening an office in San Francisco provided “a real opportunity to expand the group of people we could recruit,” said Instagram co-founder and chief technology officer Mike Krieger — who lives in San Francisco and will now work some days out of the new digs.

While parts of the Bay Area shudder at the thought of more people and traffic, some cities are happy to have Facebook’s satellite offices.

The Fremont offices, which are under construction and expected to be finished in June, are a short drive from Facebook’s headquarters. The cost of a home amid Fremont’s rolling hills is about $1 million, according to Zillow — much cheaper than Menlo Park.

“If you think about where you have this opportunity, where you are able to have a job and to buy a house down the street — where would that apply to?” said Kelly Kline, Fremont’s economic development director. Kline’s question may be rhetorical, but it bears answering: not many places in the Bay Area.

In Menlo Park, a major concern is infrastructure. Mueller, the mayor pro tem, says there will be a need for services such as new schools and fire stations, as well as transit improvements that will support the influx of workers that would come with an enormous Facebook expansion. He believes Facebook, along with the state, other large Peninsula employers and other groups, should help pay for some of the transportation upgrades.

In addition, Mueller said he hasn’t ruled out revenue-raising measures such as a payroll tax, also being explored in Google’s hometown of Mountain View, that would charge companies based on the number of employees — thus hitting large ones hard.

City officials said Facebook has generally been a good partner; Mueller said Facebook has been talking with the school district and transportation agencies about the community’s concerns.

“I believe we are presently on a good path to meeting these challenges,” Mueller said.

Facebook spokesman Harrison said the company is “committed to supporting initiatives that help reduce regional roadway congestion.” He pointed to a $1 million contribution the company made in 2016 that went toward a study on transportation improvements, including restoring a rail line over the bay that parallels the Dumbarton Bridge, in partnership with SamTrans.

Half of Facebook’s employees commute to work through ways that don’t involve driving solo, like biking, shuttles and carpools, Harrison said. He declined to comment on the company’s thoughts on a tax based on workforce size.

Menlo Park City Manager Alex McIntyre said he believes Facebook is committed to the enormous proposed Willow Village campus and has “no real concern” with Facebook looking at other places for office space.

“In the region, given the transportation challenges and housing costs (and) everything else, Facebook is realizing they might need to spread themselves out a little bit more,” McIntyre said.

Wendy Lee is a San Francisco Chronicle staff writer. Email: wlee@sfchronicle.com Twitter: @thewendylee