Actor Jamie Foxx became the latest celebrity to join the ICO bandwagon on Thursday when he promoted the token sale of Cobinhood, a free cryptocurrency trading exchange.

Foxx is at least the fourth celebrity to promote an ICO on Twitter lately. Boxer Floyd Mayweather, rapper The Game, and Paris Hilton have all run similar promotions on Twitter previously.

But investors in the cryptocurrency space are not too thrilled about the growing celebrity endorsements. They believe it's a worrying sign of a bubble and will need regulators to eventually crack down on it.

"It does remind me of the Wild West. I'm pretty sure the regulators will step in and say it's not OK," said Affirm CEO Max Levchin, who's invested in a few bitcoin-related startups, including Xapo.

Levchin, who remains bullish on bitcoin and the underlying blockchain technology, said ICOs need to be more regulated with a more streamlined procedure, and pointed out there are plenty of "fraud" and "get rich quick" schemes in the space.

Andreas Antonopoulos, an early bitcoin investor, called Foxx's tweet a good indication of "peak ICO," and called it a modern-day "shoeshine boy moment," referring to the famous Joe Kennedy quote used to describe the stock tip he received from a shoeshine boy before the 1929 Wall Street crash.

"The worst reason to make an investment is a celebrity endorsement. Unfortunately, this tactic works, and that's why they're doing it," he said.