SAN FRANCISCO (MarketWatch) — Facebook Inc. got another slap in the proverbial face Monday, when a Bernstein Research analyst raised questions about the company’s revenue and business-growth opportunities as he initiated coverage of the social-networking giant.

Analyst Carlos Kirjner assigned a rating of underperform, or sell, and set a price target of $25 a share. He ranks as one of the first major analysts to take such a glum view of Facebook FB, +1.93% .

Following the release of Kirjner’s report, Facebook fell another 82 cents a share, or almost 3%, to close at $26.90, leaving the company’s shares 29% lower since going public at $38 on May 18.

In a research note, Kirjner said that due to several factors, “It is difficult to argue for owning the stock today.”

He cited what he called “the three most important questions regarding Facebook,” as reasons for his negative view of the company:

Facebook’s ability to generate revenue growth via its display-ad inventory;

the scale and timing of growing revenue from social advertising;

and the potential value of new business opportunities based on the assets Facebook already has acquired.

Kirjner also said that he believes there is a “material risk” that over the next year, “investors will question Facebook’s ability to achieve our forecasted 2013 revenue as near-tern [sales] growth decelerates.” He currently estimates Facebook will report revenue of $6.44 billion for its 2013 fiscal year.

While the analyst remains critical about Facebook’s outlook, Kirjner wrote that the company is in a strong position, due to factors like its ability to target specific user segments and deliver ads based on authenticating users’ identities.

‘Material uncertainty’

However, Kirjner said the main issues with Facebook down the road come from having to make too many assumptions and speculating about the outlook for social advertising, as opposed to traditional display-based ads.

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“There is evidence that social advertising could prove effective in some instances. [But] we believe there is material uncertainty around the timing and extent of such upside, and that this uncertainty will not be resolved in the next 12 months.”

Because of this, Kirjner estimates that over the next year, Facebook’s revenue growth will at best stabilize, “and probably further decelerate, as will growth in revenue per user,” due to an expected shift toward mobile usage and mixed data from large-brand advertisers on the returns they get from investing in social advertising.

Also figuring in Kirjner’s price target of $25 a share is the anticipation that as many as 645 million more shares could come on the market in six months, as the post-IPO lockup period ends and company insiders can sell stock. Kirjner estimates that there currently are about 2.1 billion Facebook shares currently outstanding.

