Police have said they have searched more than a dozen locations and interviewed associates and friends of Barnes, who turned 17 in January. The ex-boyfriend of Barnes’ half-sister was the last person to see her alive, reportedly sleeping on a couch in the sister’s apartment the afternoon of Dec. 28, wearing white slipper boots she had just bought.

Authorities have called this case one of the most perplexing and most comprehensive missing person investigations in years. Police have repeatedly gone on national television, encouraged family members to speak publicly and sought help from law enforcement agencies across the country.

Police have not ruled out that Barnes was the victim of a random abduction, or that she met someone in Baltimore. What concerns detectives the most is the stunning lack of physical evidence and that after four months, not a single person has come forward with a credible tip or sighting.

Barnes, who lived with her mother in North Carolina, was visiting her half-sister in Baltimore for the Christmas holidays. The track star and honors student had planned to graduate early from high school and attend Towson University.

Police said they found nothing in her background to indicate she would run away or become a victim of a domestic dispute. They said she had no psychological or legal troubles. “She was doing what any young person would do, visiting her family, and she vanished from the face of the earth,” Detective Daniel T. Nicholson IV, the lead homicide investigator on the case, said in an interview in February.

Even without new breaks or leads, the case has taken twists. City police have complained about a lack of national media attention, saying cable shows that thrive off reporting on missing person cases have shunned Baltimore because Phylicia is black.

The missing girl’s mother, Janice Sallis, has publicly denounced the half-sister, 27-year-old Deena, accusing her of condoning alcohol and allowing men to come and go from the Baltimore apartment.

Phylicia's father, Russell Barnes, has criticized his estranged wife for speaking out, saying exposing the family rift undercuts attempts to attract attention for the search. Police say they have interviewed several men who had access to the apartment, but have not named any of them suspects in the teen’s disappearance.

Several relatives, including Deena, have gone on Internet radio shows to talk about the case; several said they were willing to take lie detector tests and told interviewers that the ex-boyfriend had hired an attorney.

Deena, a pharmacy technician studying to be a midwife, has said she met Phylicia 10 years ago at a family reunion in Baltimore. They reconnected two years ago on Facebook, and Phylicia had visited Baltimore several times.

On Dec. 28, Deena said she left for work but texted and talked with Phylicia several times during the morning. Another sister, Kelly, had planned to pick Phylicia up in the afternoon. Deena also has said she spoke to her ex-boyfriend, who told her Phylicia was asleep on the couch when he left. Kelly tried to contact Phylicia between 12:30 p.m. and 1:30 p.m. but got no response.

Deena returned to the apartment about 6 p.m. that day and found her sister missing. She called Kelly, thinking they were together, and then called police.

Detectives have blanketed her neighborhood near Reisterstown Road Shopping Center with fliers and on Jan. 4 they searched a portion of Leakin Park, without finding anything. Police used dive teams to go into streams, cadaver dogs and military helicopters that can detect heat signatures from corpses. On Jan. 21, they drained a well behind a house in Southwest Baltimore associated with one of the people who had last seen Phylicia.

Guglielmi, the police spokesman, said detectives searched a small portion of Patapsco Valley State Park earlier this winter, but wanted to return for a more extensive look when the weather got warmed and the ground thawed.