“I’m 84 years old, so staying confined to the house for protection,” wrote Marcia Savin, a children’s book author and teacher who lives alone in the Cobble Hill section of Brooklyn, on the neighborhood social networking app Nextdoor.

It was Saturday, March 21. Her prescriptions were ready at a local pharmacy, she said, but she couldn’t pick them up “because I’m not leaving the house and they have stopped answering phone.”

Soon, she said, she received five offers to to help. “None of them were people I know,” Ms. Savin said in a phone interview on Tuesday. “It’s been quite heartening. This has been the only good side to all of this — the community reaching out.”

So far, Laura Weiland, 32, has made two drop-offs at Ms. Savin’s home. Their interactions are simultaneously neighborly and distant. “I’m completely confined,” Ms. Savin said. She doesn’t open the front door. “I see the person, I flip the check through the mail slot, I tell her to leave the supplies and I drag them in,” she said.

Now she has her medicine, and her fridge is full. She is grateful to Ms. Weiland, whom she has never met without a phone, screen or door between them. Ms. Weiland, a marketing professional, described her neighbor as “lovely.”

Before the virus, Nextdoor was, to most users, something between a hyperlocal Facebook and an updated version of Craigslist. (Users must register with their real addresses, which are confirmed by mail or cellphone billing address.) It could be a good place to ask for recommendations, sell old stuff or gain traction for a local interest or cause; it could also turn nasty, or paranoid, as a space for neighbors to air grievances about anything and everything, including one another.

In recent weeks, however, some New Yorkers, many isolated and under quarantine, have logged on, many for the first time, with a more focused and urgent set of questions. Last week, Nextdoor told CNN that engagement had nearly doubled. In Ms. Savin’s neighborhood, the posts read like a diary of a neighborhood on lockdown.

There were inventory updates. The hardware store had received a fresh shipment of Lysol wipes and Purell, and a deli nearby had toilet paper. One poster with a friend who was ill was asking where to buy a thermometer; a small pharmacy had some a few days ago, wrote another neighbor.

There were also requests and offers. Did anyone have an old computer or laptop? No luck. A spare computer monitor? Available for pickup immediately. Protective gear for a risky but necessary journey? “I have a mask and gloves free,” a neighbor said. MetroCards offered for free to essential workers? Claimed right away.

An international student needed at home, with nobody to take her pet bird. An offer from a “friend of a friend,” then resolution: “I’ve just found someone through this post,” the student said. “I am so, so grateful.”

Nextdoor has added new features to the platform, including a map to which neighbors wishing to help can add their location and volunteering abilities, seizing a moment when neighborliness is both necessary and necessarily mediated. The company fast-tracked the rollout of a “groups” features, with which users can congregate around particular topics or causes. Upon opening, the app shows local announcements and general safety guidelines.

In New York, where millions of people are living under some of the country’s strictest rules, users have been posting as they see fit, unsure, as in so many other things, what a local social network is for.

There are still relics of Nextdoor 1.0: complaints about discourteous runners, unverified rumors about what the city may do next and full-on conspiracy theories. The busybodies are still there, lecturing and occasionally yelling, somehow no more helpful than before, even in this golden opportunity for giving advice.

But Nextdoor was not built to be a disaster-relief platform. Its most vital role may be in directing people to organizations and networks best suited to respond to needs as the city weighs guidelines for safely helping neighbors.

Another of Ms. Savin’s neighbors, Liz Baldwin, 31, a librarian at the New York Public Library, has used Nextdoor to spread the word about a group she started called Corona Couriers, through which bike couriers — some professionals, some just people with bikes and time — deliver essential goods to people in isolation all over New York.

The group quickly grew and now runs a digital call center and no-touch delivery service, with deliveries coordinated over Google Docs and Slack.

Shira Milikowsky, 38, who lives near Ms. Weiland, posted her own offer to help on Nextdoor. There she found a small army of others nearby who were also looking for ways to chip in. “It was people saying, ‘me too, me too, me too,’” she said.

Another of her neighbors took this energy and “ran with it,” resulting, along with the work of other organizers, and posts on local Facebook groups, in the creation of Brooklyn Mutual Aid, a group offering delivery services and social support across the borough.

“It did indeed start on Nextdoor,” said Kate Ramsey, 45, a public health professional and one of the organizers of Brooklyn Mutual Aid. The service was a good place to gather names and gauge interest. It has since grown, much like Corona Couriers, into a humming logistical operation, overseen by a group of volunteers with various personal and professional backgrounds, likewise depending on various pieces of professional and personal software.

The organization, and others like it, are discovering the limits of neighborhood social networks, which are used by a tiny and often unrepresentative slice of a neighborhood’s residents.

As such, efforts to connect with people who need the most help are turning low-tech: fliers around the neighborhood and at local essential businesses, outreach to churches and pre-existing community organizations, and calls to senior centers.

Nextdoor has also continued to function in another way: as an object of bewilderment and humor. Jenn Takahashi, 31, a tech worker in San Francisco who runs @bestofnextdoor, a Twitter account that collects strange, shocking and whimsical posts from the platform, hasn’t been too surprised by what has been sent her way.

“Conspiracy theories, people trying to lighten the mood with humor, and the bad ones — racist submissions,” she said. Ms. Takahashi also been sent lots of generous posts, including offers to run errands and face-mask giveaways.

There’s still room for more lighthearted fare. A few residents of Minneapolis circulated a call to get together and sing from their front porches, inspired by videos of quarantined Italians singing from their balconies.

One later shared the experience, which was then shared with Ms. Takahashi. “I guess a bunch of people sang last night, and I tried it tonight,” the poster wrote. “I was the only one on my block but it still felt really good, and just a little bit embarrassing.”