If it is in a post, use the Report button on the post itself to alert the mods and Robin (site owner) so that we can look into it.
If it is through a PM, then you can report it as Spam which also sends an alert to the mods so that we can look into it.
If it isn't on Pinside, there isn't much that we can do about it. The mods have a "watch out for" list but unless they are posting somewhere on here so that we can investigate and/or freeze their account, that's about all that we can do.