By day, Paul Angus is an engineer. But by night, he's Cryptonomatron: a producer of hot takes on the latest initial coin offerings who has more than 8,000 subscribers on YouTube. The 43-year-old Scot's online alter-ego is mostly a labor of love, yet it sometimes comes with an added perk: payment in digital tokens.

That's thanks to the thriving but murky world of cryptocurrency "bounty campaigns," where social media influencers get paid to promote initial coin offerings, or ICOs, by the entrepreneurs (and in some cases scammers) behind those offerings. The practice isn't new — crypto celebrity John McAfee has long been a promoter-for-hire, saying in March that he charged $105,000 per tweet. But the endorsements are playing an ever-bigger role in ICO marketing after internet giants including Google, Facebook and Twitter moved to ban cryptocurrency advertisements this year.

The proliferation of bounty campaigns is one reason ICOs are raising money at a record pace, despite the ad bans and this year's steep selloff in virtual currencies such as bitcoin. Defenders of the campaigns say they're an inexpensive way to build a brand. Critics see a breeding ground for hype and misinformation. In jurisdictions where ICOs are considered securities, promoters — also known as bounty hunters — may even risk running afoul of authorities by acting as unregistered broker-dealers.

"Once it becomes clear that financial outcomes can be manipulated not just by trading but [also by] creating perceptions through social media, regulators will take a very hard stance," said Lex Sokolin, global director of fintech strategy at Autonomous Research in London.