Twitter Chief Executive Dick Costolo called secondary markets a distraction and expects private companies will increasingly enact policies to restrict the trading of its shares on those unregulated exchanges.

Microblogging service Twitter, along with fellow red-hot social media companies Zynga and Facebook, have already had to put in place lots of policies to constrain that, Costolo told the audience at a Fortune conference in Aspen, Colorado.

In December, an investment led by venture-capital firm Kleiner Perkins valued the company at $4 billion. Since then, an $80 million investment by Andreessen Horowitz in February on the private markets valued Twitter at $4 billion, and recent transactions have accorded the company a price tag of as much as $7 billion.

Costolo also indicated Twitter was looking at options to broaden its revenue streams beyond advertising, singling out taking a cut of any goods sold via the microblogging service as a prospect. But he stopped short of offering specifics.

There's a commerce opportunity to take advantage of if we want, he said. We already see a tremendous amount of commerce on the platform.

As examples, he cited the San Diego Chargers using Twitter to sell tickets last year for a game that otherwise might not have reached the audience threshold for television broadcast, and Google selling tickets to a developers' conference.

Noting that customers now typically need to go to a third-party website to buy offers, he said: The way you would think about it is, 'how can we remove friction from the process?'

Asked about Google+, the social network launched late last month by the world's largest Internet search engine, Costolo said he believed Google would leverage their tremendous reach to pull people into the experience.

Some analysts say Google+ could take a bite out of Twitter. But Costolo said Twitter would remain focused on its own goals.

(Reporting by Sarah McBride, editing by Bernard Orr)

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