Social media site Twitter saw its shares tumble 21 percent on Thursday, despite reporting quarterly results that exceeded Wall Street expectations.
Analysts gave a mixed assessment of the company's fortunes on Thursday morning, highlighting key areas in which the microblogging company needed to improve in order for its share price to continue its meteoric rise. That rise has seen it appreciate 47 percent in the 60 trading days since its initial public offering.
Swiss bank UBS was least impressed. A team led by Eric Sheridan downgraded its view on the stock to "sell" rating from "neutral" due to negative trends in Twitter's user growth and engagement.
(Read More: Twitter skids 17% on user growth, but earnings beat)
"Given the likely forward effort to improve user growth and engagement (including product development costs), we see little potential for upside in estimates over coming quarters. Even after last night's stock correction, Twitter remains one of the most expensive stocks in our universe," the bank said in a note on Thursday morning.
Twitter posted earnings of 2 cents a share for the fourth quarter, excluding one-time items, on sales of $243 million, on Wednesday after the close.
The numbers beat expectations in a Reuters poll but the more detailed metrics had analysts scribbling into the early hours.