Link Salas, the creative director for a small technology company in New York, said he used Grindr, a social networking app for gay, bisexual, and transgender men, to learn about the places he’s traveling to and to meet men there. “I change my profile to say I am in town and looking for someone to show me around,” he said. “Some guys suggest a gay neighborhood to check out or a club,” he said. Some offer to meet in person. “The way you phrase your paragraph affects the responses you get,” he said.

The gay dating app Scruff also recently started a new service for its users, Scruff Venture, in which travelers can search more than 500 destinations, and then contact local “venture ambassadors” for advice on where to go and what to do.

And while many solo travelers may indeed be single, and thus potentially open to romantic encounters, still others are on their own because their spouses or partners are back at home, unable to make this trip.

That’s one factor that in 2016 led the dating site Bumble to expand its offerings to friendship (Bumble BFF) and, in 2017, to work-related connections (Bumble Bizz). Jess Carbino, a sociologist working for Bumble, said the company’s research showed that more of its users were using the app to meet local residents when traveling solo. “People in their 20s and 30s are in different places in their lives, so it can be hard to find someone to travel with,” she said.

Of course, personal safety is always a concern for solo vacationers. “When you don’t know the area and don’t have friends there, it’s even more important to be cautious,” Ms. Castillo said. She said she always shares with a close friend the name and phone number of the person she is going to meet, where they are going and when she expects to be back at her hotel.