New York--The co-founder of Internet advertising powerhouse 24/7 Media, Mark Burchill, has left the company, it was confirmed Thursday. Mr. Burchill was senior VP of worldwide business development at 24/7. He plans to either start a new Internet company or join a start-up in the early phases of launching. 24/7 plans to announce Mr. Burchill's successor in the near future. In his role at 24/7, Mr. Burchill was responsible for building the roster of sites on 24/7's network. He also spearheaded international development. The move comes at a time when the ad-serving industry is consolidating around a few powerful companies, and pressures to add sophisticated overall marketing capabilities are on the rise.