You can "target" a specific user only if they have attacked you, and you get a message (clipboard icon -> MORE -> NEWS).
You'll see the "Situation Report" that lists the last 20 or so events that happened to you. The report might be something like messages posted to your wall or a notice of an Attack/Raid. This "report" ages in that as new events happen, older ones disappear, so if someone's raided you, your ability to attack them will end as that report gets wiped out by newer event reports.