(ABC News) -- Less than one month ago, Christopher Cornelius was asked a very simple question, to which he gave a heartbreaking answer.

The question: Some of my friends are?

The answer from the 11-year-old New Jersey boy: No one.

But what a difference a month makes.

After his dad took a photo of the school assignment and posted it to his Facebook page, it quickly went viral. And thousands stepped up to be Christopher's friend.

His father, Bob Cornelius, estimates his son has received between 4,000 to 5,000 letters. So he's started "Christopher's Thank You Campaign" and a GoFundMe page to finance the postage and supplies for the family to respond to people who reached out to them. The goal is to raise $3,000.

"At this point, we have received thousands upon thousands of letters of support based upon the Facebook post that went viral about two and a half weeks ago," he wrote on the page. "If you recall, my son, Christopher, who is on the autistic spectrum, when asked on a school assignment to list his friends, wrote 'No One.'"

Though Christopher has received letters from people in all walks of life, "by far, the largest contingent is other children," the father said.

Bob Cornelius told ABC News, "He loves the letters and presents, and I love that conversations that have happened around dinner tables, in classrooms and in churches all over."