Here's what 6 of the most powerful Wall Streeters have to say about bitcoin

By many measures, 2017 appears to be the year of cryptocurrency, but Wall Street's most powerful players are not on board with the craze.

The market for cryptocurrencies, digital coins powered by so-called blockchain technology, is up by more than 720% since the beginning of this year, at $145 billion.

Bitcoin, the first and largest cryptocurrency, is up more than 450% since the beginning of the year. It is seen as the most crowded trade to a pool of 214 fund managers overseeing $629 billion, according to a survey conducted by Bank of America Merrill Lynch.

At the same time, initial coin offerings, a cryptocurrency-based fundraising method, have taken off with hundreds of startups using the method to raise, in some instances, millions of dollars in a matter of seconds.

On top of that, over 75 crypto "hedge funds" have popped up to invest in the more than 1,000 cryptocurrencies on the market and initial coin offerings.

The massive growth of the market has piqued the interest of folks from Main Street to Wall Street, but Wall Street's top execs - who have seen their fair share of bubbles - are concerned.

Since the beginning of the month, a number of top Wall Streeters have weighed in on the bitcoin debate. Here's what six of them have had to say: