I'm not going to say none, but I would venture a likely guess would be less than 1%.
According to Wikipedia, "About 900,000 gang members lived "within local communities across the country," and about 147,000 were in U.S. prisons or jails in 2009."
So, that's around 1,047,000 total gang members living in the US as of 2009. The 2009 US population is 306,800,000. So, in 2009, gang members made up 0.341% of the total US population.