By Tommy Wilkes and Jemima Kelly
LONDON (Reuters) - Bitcoin, the world's largest cryptocurrency, skidded 11 percent on Thursday to its lowest since late November, as a Facebook (NASDAQ:FB) ban on cryptocurrency adverts and a growing regulatory backlash against the nascent market frightened investors.
Thursday's drop to as low as $9,022 (£6,333) on the Luxembourg-based Bitstamp exchange left bitcoin trading at less than half the peak price of almost $20,000 it reached in December. It slid more than 26 percent last month, in its worst monthly performance since January 2015.
Other cryptocurrencies, including Ripple, the third-largest by market value, and Bitcoin Cash, have also racked up double-digit declines in the last 24 hours, according to Coinmarketcap.com, which tracks the industry. Ethereum was up slightly on the day.
Last year's explosive rise in the value of digital coins and the flood of new retail investors drawn to the market have rattled global regulators nervous about a sector used largely for speculation.
Officials have also warned cryptocurrencies can be used by criminals to launder money. India, which has likened the market to a Ponzi scheme, on Thursday vowed to eliminate their use..
Facebook said in a post on its website this week that it was banning all advertising that "promote financial products and services that are frequently associated with misleading or deceptive promotional practices, such as binary options, initial coin offerings and cryptocurrency".
It was not clear whether the ban would affect all cryptocurrency adverts on the social media site. Facebook could not immediately be reached for comment.
A $530 million hack of Japanese cryptocurrency exchange Coincheck late last week has also weighed on the market, along with a subpoena U.S. regulators sent to two of the world's biggest cryptocurrency players, Bitfinex and Tether.
"Sentiment towards cryptocurrencies is turning sour with negative headlines pouring out from left, right and centre," said Fawad Razaqzada, an analyst at FOREX.com
"Concerns that Facebook is banning ads and major crypto exchanges shutting down have really silenced the hype and some people are probably having second thoughts about investing their hard-earned cash into digital currencies."
In a development welcomed by cryptocurrency investors, the finance minister of South Korea, a major hub for digital coin trading, said on Wednesday there was no plan to outlaw their buying and selling after regulators had earlier pledged to do so.
Critics call cryptocurrencies a speculative mania that will end in tears for thousands of retail investors. Supporters say the price volatility is a distraction from the value of the underlying technology, which will transform the way money is stored and transferred and upend conventional banking.
"Short-term pessimism misses the point that it [regulation] could make the ecosystem thrive in the long term," said Charles Hayter, founder of London-based Cryptocompare.
International regulators are expected to debate how to address the risks posed by the market at the next G20 meeting in March.