Rachel Hope is 5-foot-9 and likes yoga, dance and martial arts. A real estate developer and freelance writer in Los Angeles, Ms. Hope, 41, is seeking a man who lives near her, is healthy and fit, and “has his financial stuff together,” she said. Parker Williams, the 42-year-old founder of QTheory, a charity auction company also in Los Angeles, would seem like a good candidate. A 6-foot-2 former model who loves animals, Mr. Williams is athletic, easygoing, compassionate and organized.

Neither Ms. Hope nor Mr. Williams is interested in a romantic liaison. But they both want a child, and they’re in serious discussions about having, and raising, one together. Never mind that Mr. Williams is gay and that the two did not know of each other’s existence until last October, when they met on Modamily.com, a Web site for people looking to share parenting arrangements.

Mr. Williams and Ms. Hope are among a new breed of online daters, looking not for love but rather a partner with whom to build a decidedly non-nuclear family. And several social networks, including PollenTree.com, Coparents.com, Co-ParentMatch.com, and MyAlternativeFamily.com, as well as Modamily, have sprung up over the past few years to help them.

“While some people have chosen to be a single parent, many more people look at scheduling and the financial pressures and the lack of an emotional partner and decide that single parenting is too daunting and wouldn’t be good for them or the child,” said Darren Spedale, 38, the founder of Family by Design, a free parenting partnership site officially introduced in early January. “If you can share the support and the ups and downs with someone, it makes it a much more interesting parenting option.”