Activists describe the crisis as a legacy of generations of government policies of forced removal, land seizures and violence inflicted on Indigenous people. Hundreds of the missing never return, and families said they have struggled to find counseling and treatment for those who do. Some are trying to cope with the trauma of being trafficked. Some are confronting addiction or grappling with violence they suffered on the streets. Some had fled abuse at home and do not have a safe place to welcome them back.

There are also authorities and counselors who have failed to screen located Navajo women and girls as victims of sex trafficking, said Amber Kanazbah Crotty, a Navajo Nation Council delegate who has been studying the issue.

On the Yakama reservation in Washington State, Larise Sohappy’s family spent three weeks looking for her after she went missing in August 2018. Ms. Sohappy, 36, said she had been “lost in my addiction” after being in an abusive relationship.

Her family rejoiced after relatives and tribal police found her, but Ms. Sohappy said she felt humiliated to suddenly be known as a Missing Person reading local newspaper articles about her family’s search. One day, she walked into a convenience store in Toppenish and saw her own “Missing” poster on the wall. But when she tried to enroll in a tribal substance-abuse clinic, she said, she was told there was a two-week wait.

“I kind of stopped trying,” Ms. Sohappy said.

She said her drinking got worse and she grew more despondent until one night in November, when she texted a suicide hotline as a last plea for help. This time, it worked. She is now in an outpatient treatment program in Portland, Ore., and taking classes in medical billing.

“While I was gone I felt like nobody loved me and nobody cared about me,” she said. “We’re overlooked as a people.”

A lack of support or follow-up from social workers or victims’ advocates makes it more likely that women and girls will go missing repeatedly. Some are written off as habitual runaways, activists said. In Washington State, Ms. Lucchesi has collected data showing that 83 percent of missing girls had been reported missing more than once.