Today there are more than 2.5 million volunteers in New York City — a figure that represents more than 300 million annual hours of service and $2.5 billion measured by time spent volunteering.

Volunteering is woven into the fabric of our great city. Since New York City’s 19th century boom and its accompanying hardships, volunteerism has met the city’s most urgent public needs and supported the impoverished in their pursuit of the American dream.

There are many individuals who serve on boards without pay. An even larger number choose to spend their time in a variety of volunteer activities, such as tutoring or serving as mentors for at-risk young boys and girls.

These numbers are impressive, but not enough to tackle the tough times we now face. Nineteen percent of residents live below the poverty level and only 52% of high school students graduate in four years. And the cost of living in New York City increases daily.

According to the Corporation for National and Community Service, when compared to the rest of the nation, New York State ranks 49th overall in both the average number of annual hours volunteered per resident and in the rate that young people perform service. In terms of New York’s level of active community engagement, a measure which includes volunteer and voting rates, New York is ranked 48th.

And yet we’ve seen how, time and again, New Yorkers respond to a crisis with outpourings of charity. No better instance of the resilient bonds holding New Yorkers together can be found than in the days after September 11, 2001, when more than 150,000 New Yorkers donated time and energy to heal our city and its people.

Working tirelessly, they searched for lost loved ones, cleaned up downtown streets, housed displaced residents, and gave money to charities. The volunteer spirit displayed on those days was quintessential New York.

As head of the United Way of New York City I have witnessed the impact that dedicated volunteers bring to a community. Those willing to set aside time for their fellow New Yorkers can do more to help individuals and families than we realize.

For example, each year United Way of New York City matches highly skilled volunteer financial consultants with low-income New Yorkers to help them build savings and increase assets. The program involves free income tax preparation, legal services related to debt, year-long financial coaching, and technical help applying for the Earned Income Tax Credit.

Our Youth Financial Empowerment Initiative pairs business professionals with young people aging out of foster care, to help train these young people in financial basics, such as how to open a bank account, establish credit, and avoid high interest scams.

As New Yorkers we share a common purpose, one grounded in strengthening our communities and lending a hand when others are in need. On Saturday, September 20th, United Way of New York City launches the “Live United” campaign with a symbolic walk across the Brooklyn Bridge to raise awareness of the need to bridge the gap in education, income, and health in our city, followed by a volunteer festival at Brooklyn’s Cadman Plaza Park.

We are asking all New Yorkers to show their solidarity by joining us and by learning more about the many volunteer opportunities available to them in their communities. It’s time we challenge ourselves to do more, inspire others to do the same, and strive to create real and lasting change in our city.

Mr. Campbell is the president and chief executive officer of United Way of New York City.