Akamai Technologies Inc., which helps businesses deliver data at faster speeds over the Internet, said CEO Paul Sagan will leave by the end of 2013. The Cambridge company is starting a search to replace Sagan, who became president in 1999 and CEO in 2005. Akamai’s sales more than quadrupled during his tenure. Sagan helped Akamai become less dependent on its content-delivery network business. He acquired firms to add services and products that would differentiate Akamai, analysts said.