Even more disconcerting, in the eyes of some analysts, was that the typical amount of time people spent checking out timelines at Twitter actually dropped.
"If you don't have an engaged user base, you don't have a business," Forrester analyst Nate Elliott told AFP.
"They have got to do better on users, that is the entire story."
Twitter makes money from ads in the form of "promoted tweets" in timelines, and it need strong growth to keep its momentum.
Twitter shares skidded more than 11 percent to USD 58.50 yesterday in after-market trades that followed its first quarterly earnings release since its stock market debut last year.
The results showed revenues in the quarter that ended December 31 doubled from a year ago to a better-than-expected USD 242.6 million.
But, investors seemed unhappy that the average number of monthly users had climbed just 30 percent to 241 million when compared to the same quarter a year earlier.
The number of worldwide users was up just nine million from the figure of 232 million when Twitter went public last November, suggesting only modest growth at a time when investors were looking for a surge.
In its first earnings report as a public company, Twitter said the loss for the year widened to USD 645 million from USD 79 million in 2012 even as revenues more than doubled to USD 664 million for the full year.
The San Francisco-based firm said advertising brought in USD 220 million in the quarter, an increase of 121 percent year-over-year, with mobile accounting for more than 75 percent of total.
Data licensing and other revenue totaled USD 23 million. International revenue jumped 200 percent to USD 66 million, an increase of 200 percent to make up 27 percent of all revenues.
Shares in Twitter soared from the offering price last November of USD 26, and analysts say that to sustain that momentum Twitter must prove it can grow and move toward profitability.
"Twitter finished a great year with our strongest financial quarter to date," said chief executive Dick Costolo said in the earnings release.
"We are the only platform that is public, real-time, conversational and widely distributed and I'm excited by the number of initiatives we have underway to further build upon the Twitter experience."
Twitter has fast become engrained in popular culture but must still convince investors of its business model.
Twitter is expected to be able to reach profitability over time by delivering ads in the form of promoted tweets, and from its data analytics.
"The problem is that there are some serious caveats for growth ahead and user metrics," Jon Ogg of website 24/7 Wall Street wrote in a post about the earnings.
"Twitter's stock is so far getting a reality check."