Bitcoin prices extended declines Friday amid one of the cryptocurrency's most volatile weeks, which saw the year's hottest investment phenomenon fall 42% from its recent peak of just under $20,000 each.

Bitcoins on the bitstamp exchange, which feeds prices into the reference rate for the CME Group's benchmark futures contract, were changing hands at $11,470 each at 9:45 am eastern time.

Specific catalysts for the moves have been difficult to isolate, given the lack of fundamental price drivers in any of the more than 1,200 digital currencies that are currently in the marketplace, although some investors have noted that cash is shifting from the loosely-regulated world of cryptocurrency exchanges into blockchain-specific stocks such as Riot Blockchain (RIOT) - Get Riot Blockchain Inc Report , Longfin (LFIN)  , and the Bitcoin Investment Trust (GBTC) - Get GRAYSCALE BITCOIN TRUST Report .

But even evidence of that change in direction has raised troubling questions about the market's sustainability after an unprofitable drinkmakers, Long Island Ice Tea Corp. (LTEA) , rose nearly 300% in a matter of hours after it changed its name to Long Island Blockchain Corp.

Investors may also be finally heeding warnings from establishment figures such as European Commission Vice President Valdis Dombrovskis, who said earlier this week that "virtual currencies like bitcoin are not really currencies" and that they can "drop at any moment".

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"In recent weeks, bitcoin has our heightened attention," he told reporters in Brussels. "There are clear risks for investors and consumers associated with price volatility, including the risk of complete loss of investment, operational and security failures, market manipulation and liability gaps."

There have also been a notable number of concerns with respect to exchange hacking and investor front-running in recent days which could be cooling some retail appetite for increased speculation over the Christmas holidays.

Earlier this week a major cryptocurrency exchange, Coinbase, said it would investigate the possibility of insider trading on its platform after bitcoin cash prices spiked to $8,500 each in the opening hours of its trading debut.

"If we find evidence of any employee or contractor violating our policies-directly or indirectly-I will not hesitate to terminate the employee immediately," Coinbase Brian Armstrong said in a blogpost.

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