When Tim Sae Koo was only 2, his parents divorced and his mother had to work two jobs to support the family. Tim’s older siblings took on the duties of raising him. “Seeing everyone do all this work for me made me feel humbled, and I knew I wanted to make them proud one day,” he said. So he founded a website in Los Angeles that links to other sites based on friends’ recommendations. Still only 21 years old, he’s won funding from an incubator and an accelerator and now has four employees. (His profile is on page 33.) But he’s only one of L.A.’s young entrepreneurs, and you can read about them in this section, the Business Journal’s annual roundup of 20 Angelenos – still in their 20s – who launched and now run their own companies.