• by Joe Mandese  @mp_joemandese, June 19, 2013

Facebook has reached an important ad industry milestone, becoming one of the few mega platforms to join the 1 million advertisers club, thanks to the rapid growth of its long tail. The news was disclosed in a corporate blog post thanking “the over one million businesses like them who are active advertisers” using the social network.

Like other members of the million-plus advertiser club, including Google, Facebook’s ubiquity is due largely to smaller advertisers, including many small business operators.

“We all start small. And whether you’re reaching your first customer or your millionth, I’m thankful that we’re a part of your business,” Facebook Director of Global Marketing Solutions for small and medium-sized businesses Dan Levy posted on a corporate blog, inviting those smaller advertisers to post their own stories about their Facebook advertising successes.

At least one Wall Street analyst greeted the hyper diversification of Facebook’s ad marketplace as a sign of strength, not a weakening of its relationship with Madison Avenue.

“While some observers might read this data as implying weakness in growth from other segments of advertisers, we view this very positively, as it speaks to the predictability and durability of the company's revenue growth,” Pivotal Research Group’s Brian Wieser wrote in a note to investors this morning.

Among other things, Wieser noted that the data reveals “a doubling of the company’s base of small business advertisers” in the past six months alone.

“If our spend-per-advertiser estimates are correct and we were to assume the numbers of business provided were comparable, we could see small businesses as representing most of Facebook's ad revenue growth this year,” Wieser predicted, adding that the revelation reaffirmed Pivotal’s confidence in its target price for Facebook’s shares, which is nearly 49% above their current trading levels.