If everyone loves Twitter, why is it sputtering?

In tweeting his message announcing the departure of four key executives early Monday, Twitter CEO Jack Dorsey highlighted one of the shortcomings of his microblogging service: the inability to send messages longer than 140 characters.

Hamstrung by Twitter's strictures, Dorsey resorted to posting an image of the text of his somewhat lengthy explanation to inform the Twittersphere of the management changes taking place at the San Francisco-based company.

Twitter (TWTR) is exploring the idea of allowing users to send messages of up to 10,000 characters, giving them much more freedom to say all that they need (or want), but that move alone won't shore up its flagging share price.

Since July 1, when Dorsey returned as interim CEO after the departure of former CEO Dick Costolo, Twitter shares have fallen nearly 50 percent (as of Friday's close) and now trade at below their IPO price. Shares fell another 4 percent in midday trading Monday.

News of the departures of engineering chief Alex Roetter, product head Kevin Weil, human-resources vice president Skip Schipper and media head Katie Stanton prompted analysts at Stifel Nicolaus to downgrade Twitter shares to "hold" from "buy."

"[W]e don't see how the departure of the heads of three major business divisions can be viewed as a positive," Stifel analysts wrote in a research note.

Other analysts were more sanguine. Writing in a research note, S&P Capital IQ analyst Scott Kessler reiterated his firm's "strong buy" rating on Twitter, citing the company's strong balance sheet and financial flexibility, which included $3.5 billion in cash and investments as of September. That gives Dorsey plenty of time -- 412 years, in fact, based on Twitter's most recent burn rate of $8.5 million in free cash during the past 12 months.

Still, Kessler said he had "concerns about the magnitude of these changes," but said that "Dorsey and [Chief Operating Officer Adam] Bain took on their current positions just a few months ago, and want to choose and shape TWTR's leadership structure and team."

Whomever Dorsey chooses to help turn Twitter around will have their work cut out for them. After a long streak of robust growth that turned it into one of the Internet's hottest companies, Twitter's subscriber growth has slowed dramatically during the past 18 months, allowing photo-sharing service Instagram, with some 400 million users worldwide, to surpass it. By comparison, Facebook, which dominates the social-media landscape, has 1.5 billion users.

Part of Twitter's problem is that many people simply don't understand how to use it or find that it's not an essential forum for communication. One example: Warren Buffett, who showed up rather late to the game when he sent out his first tweet in April 2013. Since that time, however, the Berkshire Hathaway (BRK.B) CEO has tweeted only six more times and hasn't sent a message via Twitter since last May.