If you know the member name you can search using the magnifying glass and then advanced search, then click their username to display their profile, and from there you can choose to PM (message) or email (if enabled) by clicking the envelope or bubble icons in the bottom right of the profile box.
You can list members by their location, IF they have added their location to their profile. This can be found in the top menu bar under Forum > members and sorting by clicking on 'location' and then navigating to the page where Pembrokeshire starts... around page 500...
memberlist.php?sk=b&sd=a&start=9980
once you have located your suspect, click on the user name to display their profile and from there you can choose to PM (message) or email (if enabled) by clicking the envelope or bubble icons in the bottom right of the profile box.
e.g.