NEW YORK » On an app, pins on a New York City map chart sightings of homelessness, accompanied by photos of people lying on sidewalks, slumped in doorways, sitting on curbs with shopping carts piled high with bags. Hashtags frame the scenes: “NeedsMedicalAid,” ”Encampment,” ”AggressiveBegging,” ”Violent.”

On a similar Facebook page, residents of a Manhattan neighborhood share pictures and complaints about people living on the streets, some half-naked. A website created by a police union posts pictures of the homeless and vows, “We are watching you!”

In a year of anxiety and frustration about homelessness in the nation’s biggest city, advocates for the homeless see the social media chronicling as more harassment than help. Organizers say they are only illustrating a pressing social problem to urge the city to solve it.

“People thought I was picking on the homeless,” says Ed Mullins, who heads the police sergeants’ union that maintains Peek-a-booNYC, an online photo gallery of people on the streets. “My question is, ‘Well, what can you do better?’ “

New York has the biggest homeless population of any U.S. city, according to federal statistics. As of Tuesday night, there were over 57,700 homeless people in shelters, a 13 percent increase from the same night two years ago, with possibly thousands of others on the streets.

While homelessness has declined nationwide in recent years, it has swelled in some places as rents climbed and incomes lagged, among other likely factors. Los Angeles and Hawaii both declared this fall the problem had reached a state of emergency.

New York’s street-homelessness census in February found nearly 3,200 people, down 5 percent in a year. But advocates question the count’s accuracy, and other statistics suggest street homelessness is at least increasingly visible.

The city’s 311 complaint system has fielded more than twice as many reports about homeless people in the first 10 months of this year as during the same period last year, and police have tallied about twice as many encounters with people unwilling to go shelters. And a recent Quinnipiac University poll found 61 percent of city voters disapprove of how Mayor de Blasio is handling poverty and homelessness.

His administration has noted that homelessness was already spiking when he took office in 2014 and that he has slated $1 billion in new spending on the issue over the next four years. He says over 52,000 people have moved out of shelters in the last 16 months, nearly 40 percent of them aided by rent subsidies and public-housing preferences de Blasio created or revived. The city also has helped thousands of tenants fight evictions and is adding 500 homeless-shelter beds at religious institutions this winter.

“This is going to be a big, complicated effort,” de Blasio said this month.

But some residents in Manhattan’s Murray Hill neighborhood say what they’ve been seeing doesn’t look like progress: people and possessions sprawled on sidewalks, people urinating and defecating in plain sight, men without children hanging around in playgrounds. After a convicted sex offender who had been living at a major local homeless shelter was charged with a bar-restroom rape this spring, residents took their alarm to social media in a way residents of other cities apparently have not.

A Facebook group called ThirdAnd33rd grew to 700 members, and one created a “Map the Homeless” smartphone app. Online and other activism helped spur police patrols for childless adults in a Murray Hill playground and tighter eligibility criteria for the shelter.

“It’s a way for people share photos of disturbing things they see” and push collectively for change, says ThirdAnd33rd administrator Lauren Pohl. “The intent was never to shame anyone.”

But homeless-services advocates say the photos humiliate the homeless by portraying them as an unsightly bane in forums where they’re sometimes scorned as “scum” and “human trash.”

Dave Giffen, the executive director of the Coalition for the Homeless, calls the initiatives “unethical and inhumane.” Jean Rice, who was homeless for years and is on the board at advocacy group Picture the Homeless, is concerned that they “single out a subpopulation” for scrutiny.

Mayoral spokeswoman Ishanee Parikh suggested New Yorkers concerned about homelessness use the 311 complaint system, not “apps that serve to stigmatize or harass those on our streets.”

Meanwhile, an app called WeShelter has its own approach.

Tapping a button sends a small donation, averaging about 5 cents, to homeless-service agencies from corporate sponsors. It counts over 30,000 taps in roughly nine months.

“The goal here,” co-founder Ilya Lyashevsky said, “is to really allow people who are residents of the city to be able to act on the compassionate impulse to help.”

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Associated Press writer Jonathan Lemire contributed to this report.