The social network giant's vaulation fell to $75 billion from $80 billion last month.

NEW YORK (TheStreet) -- Facebook's valuation fell to $75 billion from $80 billion in October during a recent SharesPost auction.

This is the fourth month in a row that the social networking giant has seen a decline in its valuation after hitting a peak of $87.5 billion over the summer.

Facebook CEO Mark Zuckerberg

SharesPost, a marketplace for stock of privately held companies, sold 75,000 shares of Facebook for $30 each during its most recent auction. The valuation is based on estimates that Facebook has around 2.5 billion shares outstanding.

Facebook may be looking more closely at filing for an IPO within several months, according to a report Friday on Business Insider.

Still other reports have said an IPO isn't likely until late 2012.

-- Written by Olivia Oran in New York

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