Muhga Eltigani's waist-length tresses were thin and brittle, but, while in Africa during her junior year at the University of Pennsylvania, she discovered homemade hair treatments using avocado and mango. Eltigani, a Sudanese immigrant, loved them. As she worked at a startup in 2015, she raised more than $9,000 through Indiegogo for an avocado-and-oil deep conditioner for black women with frizzy or unruly curls. A second product, derived from Jamaican black castor oil, followed, and production has outgrown the basement facility overseen by co-founder Sam Roberts. Recent funding freed Eltigani from pitch competitions, at which she's won $120,000--and Eltigani is thinking big. "I don’t see why we can't be the next L’Oréal," she says. --Leigh Buchanan

Ten years ago, if you had told Daniel Katz that he'd be running a $10 million company by the time he could drink legally, he would have probably wondered what would take so long. He started eight businesses in his teens--selling, variously, electronics, cars, snakes, a house, and energy drinks. In 2015, he started No Cow, which sells low-sugar and dairy-free protein bars, cookies, and nut butters. Last year, it attracted a "sizable" undisclosed minority investment from General Mills and Chicago-based private equity firm 2X Partners. Since then, the company, which expects to book $20 million in 2018 sales, has changed its name (from D's Naturals), revamped its packaging, and hired a CEO. It had been a one-man operation before the investment came through. "I was working 18-hour days seven days a week. Buying 10-for-$10 canned vegetables to live off of and sleeping in the office," Katz says. "It was time to get rid of my air mattress." --Diana Ransom

In 2010, 16-year-old Joe Fasone discovered what many entrepreneurs take years to realize: The best businesses solve problems. His particular pain point came to him through the then-teenager's employer, WeWork, which, at the time, was a scrappy co-working startup in New York City. By attempting to connect the growing company with reliable internet service, he realized just how hard that can actually be. It was expensive and the time it took to actually get companies to call him back was unacceptable. "I finally hit the realization that no ISP was built to deal with a company growing as fast as WeWork," says Fasone, who had already dropped out of high school to work at the startup full time. 

By the end of his four-year tenure, he had conceptualized a business that would do just that. By tapping into so called "dark fiber"--that is, underutilized fiber-optic cables that serve many of the nation's biggest cities, he says he's able to charge less for better service. Today, the 24-year-old operates Pilot, an internet service provider that caters to businesses across New York City, Philadelphia, Boston, and Washington, D.C. Pilot has 98 employees, 1,250 clients, and more than 75,000 users on the East Coast. It has also raised more than $32 million in funding. --Guadalupe Gonzalez

Raised by a single mother on government aid and having attended a struggling New York City public school, Karim Abouelnaga, 26, saw higher education as the ticket to a better life. He didn't have the scores to enter a prestigious college the first time around, but a mentor encouraged him to try again. He did--and successfully transferred to Cornell his sophomore year. Abouelnaga wanted to find a way to give back to kids with a similar background. So he gathered his friends to help launch a pilot summer school program at his high school, where the six-year graduation rate was 55 percent. At the end of the summer, Abouelnaga decided to turn the program into a business. Declining a Wall Street offer and instead raising funding from students, professors, and a handful of business pitch competitions, he founded his company Practice Makes Perfect in 2015.

Practice Makes Perfect provides summer academic enrichment programs for inner-city K-12 schools across New York City--serving over 1,300 students. But it's not just summer school. Abouelnaga aims to make the connections meaningful: The company trains students to be mentors and pairs mentors and students in the same neighborhood to help with social and emotional development. "Without the relationship piece, your attendance falters because you don't have the opportunity to build relationship with kids," he says. The company, which has 31 paying customers, charges schools based on the number of classes and duration of programs, allowing students to attend for free. About 89 percent of students successfully graduate from their summer program, Abouelnaga says. Practice Makes Perfect, which has eight full-time employees, hit $1.79 million in revenue in 2017. --Michelle Cheng

If you've ever craved a stadium-style hot dog in the dead of winter, or your grandmother's cupcakes when Grandma isn't around, Pull Up a Seat is the app for you. Camille Baker started the company after finding herself longing for more options than the fast-food chains her hometown offered. She wants to create a community of food lovers, where businesses without brick-and-mortar operations can list their offerings on a platform similar to an Etsy shop, and customers can see who's cooking around them. Baker's clients are focused on crafting the perfect taco or vegan dessert, and don't want to worry about maintaining a website, she says. "What we do is give them the software in a box, but also give them--both the customer and the vendor--the ability to find each other in a very easy way." Baker built the tech behind Pull Up a Seat all on her own, launching in August 2017 after securing an initial $40,000 from the eFactory, a startup accelerator in Springfield, Missouri. The Orlando, Florida-based company now has four employees and is looking to expand. Baker's approach to the challenges ahead? "Go out there and try to get it, and if they say no, they say no." --Sophie Downes