SAN FRANCISCO — The Facebook­ spring is over. The dog days of August have taken hold.

In May, when investors tripped over themselves to have a piece of Facebook, not even the skeptics predicted what would happen. The shares have lost more than 40 percent of their value.

The stock began to fall immediately after its debut; at first, technical glitches with the offering were blamed. But these problems do not account for the stock’s subsequent free fall, analysts and shareholders say. It can be traced to several factors, they say, among them the sheer size and price of the initial offering, early exits by major investors, and slowing growth.

Not least, the stock seems to have been jinxed by Facebook’s own fairy tale.

‘’The underwriters (and the media) did a great job of hyping Facebook leading up to the IPO, and the sell-side (including me) did a great job of hyping it after,’’ Michael Pachter with Wedbush Securities, an equity research firm, wrote in an e-mail.

Still, some investors remain bullish. Facebook is profitable, it keeps its nearly 1 billion users glued for longer than any other Internet site, and it is aggressively experimenting with ways to drum up advertising — its main source of revenue. This month, for instance, it began offering application developers a way to focus ads and sought to diversify revenues by opening its site in Britain to online gambling.

The next test for the stock could come soon. Over 1.6 billion shares will be eligible to come on the market in several waves, starting Thursday, when a number of shareholders are allowed to sell. Investors may fear that an influx of shares could cause prices to fall even more.

‘’It becomes a company perceived as vulnerable rather than invincible,’’ said David B. Yoffie, a Harvard Business School professor who sits on several technology company boards, though none that relate to or compete with Facebook.

Facebook executives say they remain focused on expanding.

One former Facebook employee, who did not want to be named because he did not want to damage his relationship with onetime co-workers, said he expected other employees to cash in their stock options as soon as they could. He predicted the stock’s woes could make it difficult to retain and hire talent. He no longer owns Facebook stock.

The public offering was pegged at a market value of over $100 billion. And the company’s growth figures seemed extremely alluring.

Facebook had raised its user base at rocket speed since its start in 2004, to 845 million in February. Revenue had swelled to nearly $4 billion in 2011 — nearly a fivefold increase in two years.

Facebook was only beginning to figure out how to make money from the stream of personal data that its users reveal about themselves.

Facebook’s stock rallied briefly in June and settled at just under $30 by July. In late July, it took a hit when Zynga, which makes games to play on Facebook and shares revenue with the company, posted weak earnings. The next morning, after­ Facebook’s own earnings report, the shares slid again. Friday’s price was $21.81.

In the end, the performance of the company is what will matter. Facebook’s immediate challenge is making money on mobile, where more than half its worldwide users are logging in. It has only recently and cautiously started advertising in the mobile arena.