Shares of Groupon Inc. fell to a record low after Barclays Plc cut the price estimate and rating for the stock, citing the potential for increasing marketing costs and narrowing profit margins amid sales of discounted items.

Chicago-based Groupon dropped 2.4 percent to $4.54 at the close in New York. The stock has lost 77 percent since an initial public offering in November. Barclays downgraded its recommendation on the shares to the equivalent of a sell, and lowered the price estimate to $4 from $15.

Groupon is one of several Internet stocks, including Facebook Inc., to come under pressure after the lifting of lock- up periods, which bar insiders from selling shortly after initial public offerings. At Groupon, slowing customer growth is leading to higher marketing costs, while an expansion beyond daily-deals into sales of discounted merchandise is threatening profit margins, according to Mark May, an analyst at Barclays.

“The majority of Groupon’s growth is coming from lower- margin product sales, and as such, the company’s business model could be undergoing a meaningful transition that persists and creates uncertainty,” May said in a research report today.

The company makes money by selling discounts -- known as Groupons -- from businesses such as restaurants and nail salons. It then splits the revenue with the retailers. Groupon earlier this month reported second-quarter revenue that missed estimates due to economic weakness in Europe.

Groupon Goods

A larger portion of sales in the quarter came from Groupon Goods, an e-commerce site for marked-down products. The service made up most of the company’s $65.4 million in direct revenue, which more than tripled from $19.2 million in the first quarter, Chief Financial Officer Jason Child said on a conference call with analysts.

A lock-up for Groupon shares expired on June 1, the company said in a May regulatory filing.

Groupon backers Battery Ventures and Andreessen Horowitz have divested their stakes, joining a group of early investors who have sold the stock, contributing to a continued slump.

Battery sold all of its 15.99 million shares earlier this year, according to data compiled by Bloomberg. Andreessen Horowitz sold its 5.1 million shares in June, said a person with knowledge of the matter, who asked not to be named because the sale wasn’t publicly disclosed.

Other pre-IPO investors who have sold Groupon include Fidelity Management & Research, which trimmed its stake by 6.2 million shares to 13.2 million in the quarter ended in June, according to data compiled by Bloomberg. Maverick Capital reduced its holdings by 4.35 million shares to 1.98 million over that period, the data show. Kinnevik Investment AB said in June that it divested its direct holding in Groupon of 8.4 million shares.