Twitter is upwardly mobile.

CEO Dick Costolo offered up a little fact that certainly wasn’t lost on a rival like Facebook — that his microblogging site makes money on mobile advertising.

“It’s already been the case a couple weeks ago that mobile ad revenue in a day was greater than non-mobile,” Costolo said earlier this week. “Mobile revenue is already doing delightfully well.”

Revenue from mobile is an increasingly important metric for tech firms small and large, as more people access social media sites and other online content through smartphones and tablets.

Facebook has been under pressure from Wall Street and within its own ranks to figure out how to leverage its mobile platform, where the company has yet to make any money, a fact that was a glaring weakness when the company went public last month.

Costolo was speaking at a conference in California this week when he addressed Twitter’s business.“We’re born of mobile,” he said.

The revenue comments come as Twitter’s stock has lost value on private markets, where shares are down at least 15 percent.

Twitter is just one of the companies feeling the burn of Facebook’s botched initial public offering.

Facebook stock is down more than 30 percent since its $38 IPO. It closed down 1.9 percent yesterday to $26.21.

Also this week, Twitter insiders said the company expects to crack $1 billion in revenues by 2014 — far ahead of analysts’ estimates.