“It seems like the number of people who come to visit their families is decreasing, and the number of people who never had kids is increasing,” Mr. Schoeb said. “At some point, the loneliness is coming at you like a train coming down the tracks.”

For those with families, there can be other dangers. Older adults are more likely to experience abuse around the holidays from someone they trust, according to the New York City Department for the Aging.

The department, which explored the issue in a 2011 study, did not indicate why elder abuse is more prevalent this time of year, but it said that reports of financial exploitation and physical, verbal and sexual assaults had remained high over the years. Nearly a third of elder abuse cases reported around the city in the 2018 and 2019 fiscal years occurred from November to January, when families were more likely to be together, according to department officials, who on Wednesday announced a public campaign warning people about the trend.

“So far this year, there have been 1,623 cases reported to our elder abuse programs, displaying a pattern that must be changed,” said Lorraine Cortés-Vázquez, the department’s commissioner in an email. “If you are not reporting elder abuse because you are scared, you have another option and we are here to help.”

The woman in Tulsa, who identified herself only as Carrie, said she had been fighting cancer and was estranged from her daughter, who has refused to let her see her granddaughter even though both live close by.

“I really thought the feeling would go away, but my heart is so broken,” she said in an email. She posted the ad on Dec. 11, then went to her granddaughter’s dance studio and sat outside, hoping to catch a peek of her through the window.

When she checked Craigslist later that night, she was horrified by the responses to her ad.

“I couldn’t understand why people I don’t know were being so rude and hateful to me,” she said. “I was crushed.”