Yes, 'knows everyone here' is a stretch, but not entirely impossible. Depending on what is being posted (knowledge beyond public dissemination) and by whom, LE can submit for a warrant to ping trace to a source, whether that be through to a proxy (typically off-shore, out of jurisdiction, anonymous) or through to the originating ISP / customer's modem / then-assigned DHCP (or in some cases, static) address. Of course, such procedures are very tedious and time consuming. If LE does not use adequate software and expertise, perusing I.P. addresses in web server and router logs eats up many hours. LE also would have to submit for a warrant to the suspect's ISP, and possibly for intermediate carriers or servers, depending on routing. In some cases a warrant is immediately useless if the targeted communications route through particular off-shore servers.