Dale Pollekoff, 71, moved to Los Angeles after a long career in graphic design in Washington D.C. As a single woman with no children, she felt drawn to the city’s weather and the less conservative ideas of varied lifestyles. “I feel more like I can be me here,” she said.

But soon after her move in 2000, she ran into the challenge of meeting people to explore her new home with. “When you’re middle-aged, you make friends in your job,” Ms. Pollekoff said. “After that, it’s very, very hard.”

Los Angeles also doesn’t make relationships easy. The city is vast, and the traffic is unforgiving and constant. People often talk about the perils of dating and meeting people in major cities as young adults, but it can be just as hard for an older demographic, who according to many of the women in the group, feel largely ignored.

In 2015, after failed attempts to find a group focused on female friendships, Ms. Pollekoff decided to start her own group, called Finding Female Friends Past Fifty on Meetup, a site where people can make online groups to meet up in real life. After just a couple of weeks, the group amassed around 200 members. And it just kept growing. Today, the group has more than 800 members.