Three years after founding bitly as a home-grown startup inside betaworks , John Borthwick is passing the reigns to a new CEO, Peter Stern . Borthwick will remain CEO of betaworks and concentrate on new products and investments. Stern comes most recently from Zenbe, a webmail platform and mobile that went through a Facebook talent acquisition last November. Stern, who was a co-founder, didn't go to Facebook. He's more a New York kind of guy. Back in the 1990s, he founded Datek, one of the original online brokerages.