As his Twitter Inc. colleagues were celebrating the company’s initial public offering this month, J.J. Hirschle was gearing up for a bigger milestone: the holidays.

Hirschle, who joined from Google Inc. in October, is Twitter’s first executive responsible for targeting retailers to advertise on the microblogging service — which is especially important during the most lucrative shopping season of the year. So far, the 40-year-old has held meetings with Best Buy Co. Inc., Target Corp. and other potential clients, pitching Twitter as a platform for product marketing.

Hirschle’s mission is urgent. Twitter lags behind Facebook Inc. in dollars flowing from retailers, who are critical for the San Francisco-based company to win over following its blockbuster IPO. Retailer outlays on digital ads, which made up 22 percent of total spending in 2012, are projected to swell to $13.5 billion by 2017 from $9.4 billion this year, according to researcher EMarketer Inc.

Twitter’s stock has continued to trade well above its $26-a-share IPO price. The shares rose 2.9 percent to $40.18 at the close Tuesday in New York. But a Bloomberg Global Poll this month found 68 percent of investors surveyed anticipate the stock will be below its first-day close of $44.90 in six months.

Hirschle faces significant challenges in his new role. According to an August poll by Shop.org, when retailers were asked what significant social marketing investments they made ahead of the holidays, 34 percent said Facebook, 28 percent said Pinterest Inc., 19 percent said Facebook’s Instagram — and only 15 percent said Twitter.

Gilt Groupe Inc. Chief Marketing Officer Elizabeth Francis said the online retailer spends more on Facebook than any other social media platform. Even so, it uses Twitter to have customer-service conversations, vs. Facebook as a driver of traffic and sales.

“For Twitter it’s really about the real-time conversation that’s happening on the fly,” said Francis, whose company has been advertising on both sites since 2010. On Nov. 29, which is the post-Thanksgiving shopping day known as Black Friday, Gilt plans to run a Twitter ad campaign with the hashtag #carpeholiday that will give fans varying amounts of Gilt store credits.

At The Year Ahead: 2014 conference hosted by Bloomberg LP last week in Chicago, Martin Sorrell, CEO of global advertising firm WPP, said he sees Twitter as “primarily a public relations medium.” By contrast, Facebook is “a wonderful long-term branding medium,” he said. “It will soon be the largest country on the planet, if you think of it that way.”

Twitter has taken steps to tell advertisers that its ads can convert from eyeballs into actual purchases. In an early October blog post, Twitter cited data from Crimson Hexagon that said holiday shopping conversations on its service increased by 30 percent in 2012 over 2011.

In August, the company hired Nathan Hubbard, the former president of Ticketmaster Entertainment Inc., to help make it easier for users to shop via its 140-character messages known as Tweets. In September, Twitter also agreed to acquire MoPub Inc., a mobile-advertising exchange, to sell ads around the Web.

Those efforts remain in the early stages.