Catherine Cook, 18, is seen here with brother and cofounder of myyearbook.com, Dave Cook, along with their brother Geoff Cook.

The story of Megan Meier is unforgettable for me and many of our viewers, no doubt; a 13-year-old girl who killed herself after being harassed online. As I kept reporting the horrific details, I wondered about a solution. It turns out 18-year-old Catherine Cook was thinking the same thing.

Catherine started myyearbook.com, the third largest social network in the United States, according to Hitwise, a competitive intelligence service. Reaching out to young people online, she decided to spend the month of June educating and acting to stop cyberbullying. So far, some 200,000 teens have pledged to “think before they click” and learn how to respond if they are the target of a cyberbully. Catherine hopes to have 1 million people sign the pledge in 2008.

“While nothing can bring Megan back, knowing that 1 million young people will take a pledge against cyberbullying in her name gives me hope,” says Tina Meier, Megan’s mom.

Update: Watch the CNN.com Live interview

Ayna Agarwal, 15, founded Stop Animal Overpopulation Together Globally.

Ayna Agarwal will never forget the day she was visiting her family in New Delhi, India and she saw a helpless dog in the street. It was like so many she had seen there with infections, disease and missing paws. But, it was the last one she wanted to see without doing something about it.

Ayna started SPOT, or Stop Animal Overpopulation Together Globally, to spay and neuter cats and dogs worldwide, specifically in third-world countries. She sits on the board of The Humane Society’s youth division, Humane Teen, where she represents her passion for animal population control with other young people who are concerned with different issues like animal cruelty and fighting fur production. Trying to impart the issues she discusses there with others in her hometown of Edison, New Jersey, Ayna is now running a summer camp called Paws and Claws to educate kids in grades 3-5 about animal welfare and protection.

At 15, Ayna knows exactly what she wants to be when she grows up — a veterinarian and animal activist. She says she would like to eventually “speak for the animals because they can’t speak for themselves.”

Update: Watch the CNN.com Live interview

Aaron Arnold, 29, is the founder of Music is My Business.

No matter how old we are, no matter what stage we’re at in life, we all tend to wonder, “If money didn’t matter, what would I do?” Aaron Arnold had those thoughts. And he’s acted on them.

After Arnold graduated from college, he was fast-tracked into an executive position at a major PR firm. He had money, but he was miserable. The real answer to his nagging thoughts about his true passion was music. So shortly after he got married, Arnold took a major leap to a nonpaying (to the dismay of his wife) internship with Bad Boy Records.

He worked for free to soak up all he could as an assistant to record producer and entrepreneur Sean “Diddy” Combs. After a year of grooming, the 29-year-old went on his own to start Music is My Business. “I wanted to change the music industry for the better,” Arnold said. He now handles budding artists, with the goal of changing the way business is done in the music industry.

Update: Watch the CNN.com Live interview

Tiffany Tucker, 25, is the founder of Redemption, a youth empowerment organization based in Brooklyn, New York.

Tiffany Tucker’s smile beats her into any room. Her smile gets even brighter when she says, “the door is always open!” That door refers to one that goes into her brainchild, Redemption.

She thinks everyone in her community in Brooklyn, New York, including herself, deserves the chance to be saved or rescued. Tucker, 25, was raised by a single mom, and she knows that New York City’s streets can be mean. But she didn’t let them swallow her, and if it’s up to her, no other young person will be swallowed, either.

Redemption promotes self-esteem and leadership skills for kids 13 to 19 years old. Tucker’s program has offered more than 3,000 urban kids and teens life skills workshops, college coaching and one-on-one counseling. According to Tucker, her open-door policy has led to a huge success rate: 85 percent of students in the mentorship program have graduated from high school and signed up for higher education.

Update: Watch the CNN.com Live interview

Zac Sunderland, 16, plans to sail around the world in a boat that he and his father fixed up.

Some dreams, it seems, probably will remain just that: distant, whimsical, cinematic adventures. That’s what you probably think when “sailing around the world” comes to mind. Not so for 16-year-old Zac Sunderland.

Zac wants to set a record for being the youngest person to sail around the world solo, and he hopes to complete the journey before he turns 18. He grew up sailing and is about to set off on a well-researched trip that will take him to Micronesia; Cape Town, South Africa; and through the Panama Canal in a boat he fixed up with his dad.

Throughout his journey, Zac will be blogging. Aside from his dad meeting him at strategic locations along the way, Zac will be alone. He will have a gallon of teriyaki sauce he’s already bought in anticipation of catching his meals, along with malaria drugs, a gurney-like bed and, after it’s all over, he hopes, a record.

Update: Watch the CNN.com Live interview