NEW YORK ( TheStreet) -- After spending 40 days in silence, some analysts erupted with concerns about Facebook's ( FB) ability to generate revenue from mobile and online advertisements. Wednesday marked the end of the "quiet period" for the 33 so-called bulge-bracket banks involved in underwriting Facebook's initial public offering.
Some analysts bearish about Facebook's potential
BMO Capital Markets, which sold about 421,000 shares in the offering, was the most bearish among the banks initiating coverage. BMO rated shares "underperform," the equivalent to sell, with a price target of $25. Credit Suisse, responsible for selling 9.47 million of Facebook shares, also was relatively bearish about the Menlo Park, Calif.-based social network, initiating coverage with a neutral rating and a $34 price target. Credit Suisse analyst Spencer Wang doubts Facebook's ability to monetize mobile usage and, like BMO Capital Markets analyst Daniel Salmon, questions the effectiveness of social advertising. "We anticipate that the rate of growth in mobile usage for Facebook will exceed the growth in usage through desktop for the foreseeable future," Wang wrote. "However, Facebook does not currently generate any meaningful revenue from usage on its mobile products, and its ability to do so successfully is unproven." Wang believes that Facebook is well positioned in the space to continue capturing growth in social media, as well the ability to monetize its opportunities outside of advertising, but is cautious about valuation at these levels, suggesting limited upside. Facebook's current valuation is 23 times 2013 enterprise value over EBITDA. Despite the release of positive studies from marketing research firms, both Wang and Salmon remain unconvinced Facebook will be able to generate revenue from the evolving and highly competitive market of online advertising. "A risk exists that in the longer-term Facebook's ad products do not meet buyer expectations relative to alternatives," Wang mentioned in his note. Credit Suisse's Wang also cited concerns over potential loss of revenue from Zynga ( ZNGA). "The health of this revenue stream is contingent upon Zygna maintaining its level of engagement with Facebook's users and Facebook's ability to continue monetizing this engagement," he wrote. Zynga generated 15% of Facebook's revenue in the first quarter of this year, according to a company filing. Online video is another area where Facebook is lagging, and Salmon suggests Facebook launch "rich media or online video ads" to compete with Google's ( GOOG) YouTube and Hulu. Wang mentioned the growing importance of social media, highlighting that Facebook accounts for 17% of time spent online compared to 10% just 3 years ago. "Social media now eclipses activities such as e-mail, gaming, and instant messaging," he penned. The analyst adds that Facebook's network effect or user data, "which can act as a competitive advantage and a self-reinforcing virtuous cycle," will be difficult for competitors to replicate. Shares of Facebook were lower in Wednesday trading, off 2.87% to $32.15. --Written by Nathalie Pierrepont in New York. >To submit a news tip, send an email to: email@example.com. Check out our new tech blog, Tech Trends. Follow TheStreet Tech on your wireless devices. >Contact by Email. Follow @nrpierrepont