Facebook's 28-year-old founder and chief executive Mark Zuckerberg is expected to ring a bell at the company's Silicon Valley headquarters today to kick off the social network’s trading on New York’s Nasdaq.

Investors are bracing for Facebook's Wall Street debut, after the world's number one online social network raised about $16 billion in one of the biggest initial public offerings in US history.

Valued at $104 billion, Facebook is larger than Starbucks and Hewlett-Packard combined, sparking intense speculation on how much higher its valuation will rise once shares start trading.

"A 15 to 20% pop is in the realm of possibility," said Tim Loughran, a finance professor at the University of Notre Dame.

"Given they already moved their IPO range up and increased the size, that's bullish to begin with."

Facebook priced its offering at $38 a share on Thursday, but the price could be higher when shares begin trading under the FB symbol on the Nasdaq at around 11 am Eastern Time in the US.

Some expect shares could rise 30% or more on Friday, despite ongoing concerns about Facebook's long-term money-making potential. An average of Morningstar analyst estimates puts the closing price for Facebook shares tomorrow at $50.

The IPO, expected to mint more than a thousand paper millionaires at the company, has received wall-to-wall media coverage and sparked hopes of a boom in sales of everything from San Francisco Bay Area real estate to automobiles.

Founded in a Harvard dorm room in 2004, Facebook has grown into the world's dominant social network with 900 million users.

At $38 a share, Facebook would trade at over 100 times historical earnings versus Apple 14 times and Google Inc's 19 times.

For all the high expectations surrounding Facebook, the company faces challenges maintaining its growth momentum.

Some investors worry the company has not yet figured out a way to make money from the growing number of users who access Facebook on mobile devices such as tablets and smartphones. Meanwhile, revenue growth from Facebook's online advertising business, which accounts for the bulk of its revenue, has slowed in recent months.

"With mobile usage growth exceeding desktop, monetization in the near term could be reduced given little-to-no ad coverage on mobile, challenged by limited screen sizes," said a report last week from Susquehanna Financial Group.

GM also said Tuesday it would stop placing ads on Facebook, raising questions about whether display ads on the site are as effective as traditional media.

African perspective

Investors and traders in Africa could find it difficult to purchase shares of the social network today, according to Arthur Goldstuck, the managing director of South African-based World Wide Worx.

“Unless you are being offered shares by one of the sponsoring companies in terms of the listing process, you have to buy them in the open market,” said Goldstuck.

Goldstuck further added that buying Facebook shares today could be a highly risky move.

“I think today would be the worst day to buy them on the open market.

“You have no sense of how the share will actually perform, whether its going to hold its value, whether its going to plummet or whether it will keep rising; so, I think people who simply want the share that’s fine for them to invest, but to speculate on the share today is quite dangerous.”