I had the same question about ICO's in general. I could not find that it is unlawful or a crime for a US citizen to participate in an ICO.
Information on
https://www.sec.gov stresses caution and ways of vetting the company and promoters of an ICO to have the best chance of success in the investment.
It seemed to be the opinion of the SEC that when investments are particularly risky, participation should be limited to those who had resources that could withstand losses. This person is described as an "accredited investor". Someone who has sustainable income of $200,000 per year with proof of two years income at that level. Or they have personal wealth of $1,000,000, not including personal residence. This has to do with sales of products considered to be securities.
I felt it was useful information. Hope this helps..
