They spread out across 11 beach towns, like a hundred flecks of hope on a desperate quest: combing a stretch of the Jersey Shore for Sarah Stern, a 19-year-old from Neptune City who had been missing for a week.

Among the search party of family, friends and neighbors who braved the freezing cold in December were two high school friends of Ms. Stern’s, Liam McAtasney and Preston Taylor. Mr. Taylor had taken Ms. Stern to the junior prom. Mr. McAtasney had listed her under the “family” section of his friends on Facebook.

Ms. Stern’s body has still not been found, but now Mr. McAtasney, 19, has been charged with her murder, based on a recorded conversation with a friend. Mr. Taylor, also 19, was charged with helping to conceal the murder and discard her remains.

“It was kind of a shock, to say the very least,” said Michael Stern, Ms. Stern’s father, recalling how he felt when he learned that the two men — who had been her friends since grade school — had been accused in her death. At the initial hearing, he fought back tears, despondent that his only daughter was dead and had not simply “left without telling anybody.”