Updated from 10:42 a.m. to include analysis about lockup in the sixth paragraph.
Shares of Twitter plunged in Tuesday trading, falling 14.9% to $32.97, after having hit a high of $74.73 in December of last year.
An additional 480 million shares are now eligible to be traded, as the micro-blogging social network allows early investors and employees to sell shares, following the company's initial public offering in November. At the time, San Francisco-based Twitter sold $1.8 billion worth of stock at $26 a piece.
Currently, there are 205 million shares of Twitter available for trade.
The lockup expiry comes after Twitter reported first-quarter earnings that saw the company beat Wall Street estimates, but concerns about user growth continued to weigh on the stock. In recent weeks, CEO Dick Costolo has said that he, as well as co-founder Jack Dorsey and early investors including Benchmark Capital and others would not sell their shares with the lockup expiry coming up, as a sign of confidence in the nascent social networking company.
In a research note following the company's earnings last week, SunTrust analyst Robert Peck estimated that of the 480 million shares eligible to trade, around 200 million could be available for sale. "We estimate that ~275m shares are attributed to holders that have disclosed they will not be sellers at the lockup, leaving ~200m available for sale which could pressure the stock if certain sellers wish to monetize the ~45% upside in the shares compared to the $26 offering price.