Facebook Inc will offer its first dating service, Chief Executive Mark Zuckerberg said on Tuesday, signaling the entry of the world's largest social network into a growing market that sent shares of established dating site operators tumbling.

Zuckerberg told software developers at Facebook's annual F8 conference that a dating service would be a natural fit for a company that specializes in connecting people online.

"There are 200 million people on Facebook that list themselves as single, so clearly there's something to do here," Zuckerberg said.

Facebook users have been able reveal on the network whether they are single or in a relationship since it first went live in February 2004.

Zuckerberg said Facebook was building the dating service with an emphasis on privacy, a sensitive subject for people who use online dating and for Facebook as the company reels from a scandal over its handling of personal information.

A dating service could increase the time people spend on Facebook and be a "big problem" for competitors such as Match Group Inc, said James Cordwell, an analyst at Atlantic Equities. Match, the owner of popular mobile dating app Tinder and OkCupid, calls itself the "global leader in dating" on its website.

"But the initial functionality looks relatively basic compared to those offered by Match's services, so the impact Facebook has on the dating space will be down to how well it executes in this area," Cordwell said.

Match Group shares fell more than 23 percent on the news of Facebook's service. IAC, Match Group's parent company, dropped more than 15 percent. Sparks Networks, owner of JDate and ChristianMingle, fell 7.3 percent.

A prototype displayed on screens at the F8 conference showed a heart shape at the top-right corner of the Facebook app. Pressing on it will take people to their dating profile if they have set one up.

The prototype was built around local, in-person events, allowing people to browse other attendees and send them messages.

It did not appear to have a feature to "swipe" left or right on potential matches to signal interest, as Tinder and other established services have.

The feature will be for finding long-term relationships, "not just hook-ups," Zuckerberg said. It will be optional and will launch soon, he added, without giving a specific day.

Facebook Chief Product Officer Chris Cox said in a separate presentation that the company would share more over the next few months.

Cox said he had been thinking about a dating feature on Facebook since 2005, when he joined the company about a year after its founding.

The company began seriously considering adding a dating service in 2016, when Zuckerberg posted on his Facebook page a photo of a couple who had met on the network, Cox said.

Thousands of people responded to Zuckerberg's post with similar stories about meeting partners on Facebook, Cox said. "That's what got the gears turning," he said.

People will be able to start a conversation with a potential match by commenting on one of their photos, but for safety reasons that Cox did not specify, the conversations will be text-only, he said.

Facebook executives were quick to highlight other features for safety and privacy, noting that dating activity would not show up in Facebook's centerpiece News Feed.

Concerns about privacy on Facebook have grown since the social network's admission in March that the data of millions of users was wrongly harvested by political consultancy Cambridge Analytica.

A dating service "represents a potentially challenging situation if Facebook can't fulfill its promise to offer dating services in a privacy-protected and safe way," said Debra Aho Williamson, an analyst at eMarketer.

However, "I'm sure it will make good use of the data Facebook has been able to collect about its users," she added.

Zuckerberg also said on Tuesday that Facebook was building a new privacy control called "clear history" to allow users to delete browsing history, similar to the option of clearing cookies in a browser.

Reuters