ISTANBUL—In this ancient city once ruled by sultans and emperors, the real king is the humble alley cat.
In historic neighborhoods along Istanbul’s Bosporus and Golden Horn waterways, an army of furry-tailed street cats are fed, sheltered and cooed at by an adoring public. Hundreds of fleece-lined houses have been erected at street corners by cat-mad residents. Most are flanked by makeshift feeding stations fashioned from yogurt pots or plastic bottles and overflowing with tasty scraps.
In some districts, ground-floor windowsills are lined with pillows and blankets, offering a cozy place for the discerning kitty to recline. In restaurants and cafes, cats are often part of the furniture, curling up next to dining tables or patiently waiting for leftovers from patrons.
Visitors to the city can dine at one of several cat-theme cafes or stay a night at the Stray Cat Hostel. During a 2009 visit here, President Barack Obama paused to pet Gli, one of dozens of cats living in Hagia Sophia, Istanbul’s most famous mosque.
Now, Istanbul’s feline fetish is adapting to the digital age.
Social media sites offering daily pictures of the city’s cutest street cats boast tens of thousands of followers. Web developers have created apps to help adopt and locate users’ favorite kitties. Local filmmakers have released a trailer for their coming feature film “Nine Lives” on video sharing platform Vimeo. Wildly popular YouTube tutorials show Istanbul residents how to build shelters and feeding stations so cats can nap and nibble in maximum comfort. The #catsofistanbul hashtag on photo-sharing website Instagram has more than 50,000 posts of cats nonchalantly—and almost always adorably—doing their thing.
Ms. Babac, who currently doesn’t have a cat because of “constant travel commitments,” says her sites have morphed from a picture-sharing feed into a news portal and information exchange for cat junkies. The site also helps members coordinate with charities to improve cats’ welfare: In June members of the group joined forces with local architects to repair dilapidated cat shelters.
“Cats have always been famous in Istanbul, but social media is making them famous around the world,” Ms. Babac said.
Historians here say the social media explosion is simply the latest incarnation of a centuries-old cat craze: stemming from a combination of religion, tradition and practicality.
The feline fetish is also functional: In the 19th century, cats were bred in large numbers for pest control to kill a rat population thriving in the city’s expanding sewage system. Before that, they helped Istanbul avoid the worst of a bubonic plague epidemic spread by rats.
Cats are even hard-wired into the city’s iconography and political culture.
In the bowels of Istanbul metro stations, pictures of waterside cityscapes feature cats posing alongside fisherman, in some cases munching the daily catch. Cat cartoons are used to satirize politicians: a digitized picture of a mustachioed sour puss named Recep Tayyip Erdocat was shared thousands of times last year, in a not-too subtle effort to lampoon Turkey’s pugilistic President Recep Tayyip Erdogan.
In 2012, Mr. Erdogan’s ruling Justice and Development Party tried to pass legislation it said would improve sterilization and clear the streets of stray animals, but the plan was shelved after 30,000 people took to Istanbul’s streets in protest.
Now, local authorities say the number of street cats in the city center is growing again thanks partly to online campaigns that are helping to improve care and prevent disease.
Ground zero for the city’s cat obsession is the district of Cihangir, a liberal neighborhood where gangs of multicolored cats can be seen roaming at intersections, lounging in cafes or sunning themselves on the hoods of cars. Local restaurants and butchers work with animal shelters to make sure leftover scraps are given to strays. On one road, an abandoned blue BMW has for years been used to help local alley cats: functioning as a food store in the summer and a shelter in winter.
“A lot of our work is with strays because there are so many in Cihangir,” said Ozge Sahin, a vet at Anipoli clinic, which recently constructed a “stray hostel” where sick and injured animals can recuperate in comfort. “This area is special for animals,” she said.
Even some of the foreigners who have moved to Cihangir have adopted its cat-friendly culture.
U.K.-born resident Hilary Sable—a teacher who has five cats and feeds dozens more every day—formed the Cool for Cats association in 2011 to help care for street cats in the area.
“This online buzz is helping us to grow our network and bringing cat lovers together,” she said.
Some local businesses say they feel a responsibility to help preserve the city’s feline affinity. Pizza Factory, a trendy new food place, proclaims an “open-door policy” for street animals and sifts through leftovers to pick out waste that could upset a cat’s stomach.
“Istanbul is a heaven for cats, and we want it to stay that way,” said owner Nial Yigittas. “We recently adopted a stray and named him Azman—it means Monster.”