Dominick Quartuccio was concerned about his libido, which he’d noticed was slowing down as he reached 40. “The prevailing social narrative is that you’re getting old, so go get a pill,” Mr. Quartuccio said. An executive coach, he helps clients speak candidly about their anxieties — romantic and sexual, sometimes, as well as professional — and preferred to do the same.

Last March, Mr. Quartuccio posted on the Kaleidoscope, an invitation-only Facebook group where nearly 3,000 participants post questions and answers about sex and sexuality.

Within hours, he had more than 15 suggestions: “embracing, supporting, offering ideas — ‘hey go check out this person for reiki or tantra,’” Mr. Quartuccio said. “But most useful was the acknowledgment of my courage to talk about it. To take these shadowy conversations out into the open and demystify them.”

According to a recent fact sheet from the Guttmacher Institute, a nonprofit devoted to reproductive health, in 2014 fewer than half of American high schools and only 20 percent of middle schools taught students all 16 topics that the CDC considers “essential” to sexual health education. Between 2011 and 2013, the vast majority of teenagers 15-19 reported discussing at least one sex education topic with a parent. But those conversations vary notoriously in quality.