Twitter Chief Operating Officer Dick Costolo (@dickc) has been outlining Twitter’s plans for its new advertising system and addressing concerns about the company’s long-term monetization goals.

“We were valued at over a billion dollars last September, so we’re going to live in a world where we need to be generating hundreds of millions of dollars in revenue,” Costolo told Reuters. “We’re thinking about big, big numbers.”

Other points of interest:

• Twitter is currently adding another dozen advertisers to their Promoted Tweets platform, which Costolo says has been “successful beyond our wildest dreams.”
• Costolo says Twitter will start to “ramp this up aggressively” beginning in the third quarter of 2010
• The long-hyped premium Twitter accounts are due this July or August

Costolo: “I’m super confident but it’s a dark tunnel and we’ll see where we are at the end of Q4.”

(Source: Reuters.)