> Were these sites only (or primarily) discussion boards?
As many pointed out above, no. The majority of the forums looks to be advertisements for prostitution [0].
> Were they also used (with or without their operators' consent) to conduct illegal sex trade?
According to the FBI, "the website hosted advertisements for prostitutes, complete with explicit photos, lewd physical descriptions, menus of sexual services, hourly and nightly rates, and customer reviews of the prostitutes’ services" and the owner "engaged in more than twenty monetary transactions to launder the profits derived from the facilitation of prostitution" [1]. They are now looking to forfeit $5 million of those profits.
> If such activities were indeed happening without a site operators knowledge or consent, did law enforcement reach out to these operators in an attempt to curtail this activity?
While I couldn't find a source directly saying weather they did or did not, I would imagine it to be very difficult to collect enough evidence to go through with the forfeiture and trial while the future defendant knows they are being investigated.
The money laundering charge can be used to coerce the owner in to pleading guilty to whatever else they want to add to the list -- whether or not there is a case for it. Considering the age of the site, one would speculate that the owner may have said no to something the government politely asked for, and then ended up getting their insides turned out as a result.
The EFF certainly could have done a better job on this one. I'm not familiar with the site, but this seems to be a very different situation than Craigslist ran in to.
As many pointed out above, no. The majority of the forums looks to be advertisements for prostitution [0].
> Were they also used (with or without their operators' consent) to conduct illegal sex trade?
According to the FBI, "the website hosted advertisements for prostitutes, complete with explicit photos, lewd physical descriptions, menus of sexual services, hourly and nightly rates, and customer reviews of the prostitutes’ services" and the owner "engaged in more than twenty monetary transactions to launder the profits derived from the facilitation of prostitution" [1]. They are now looking to forfeit $5 million of those profits.
> If such activities were indeed happening without a site operators knowledge or consent, did law enforcement reach out to these operators in an attempt to curtail this activity?
While I couldn't find a source directly saying weather they did or did not, I would imagine it to be very difficult to collect enough evidence to go through with the forfeiture and trial while the future defendant knows they are being investigated.
[0] https://web.archive.org/web/20130319123304/http://forum.myre...
[1] http://www.fbi.gov/sanfrancisco/press-releases/2014/californ...