[hook] grabbing userid

[Dr.CustUmz]

first what im trying to do: I want to be able to grab the userid and show it in the forumhome_lastpostby template.

what ive got so far: i have created a plugin at forumbit_display:

$username = $lastpostinfo[lastposter];
$lastposter = $vbulletin->db->query_first("SELECT userid FROM ". TABLE_PREFIX ."user WHERE username = \"$username\"");

so its grabbing the last posters username, and looking for their id in the DB then displaying when i use

$lastposter[userid]

the problem is, it's not quite working =(

i get a result that shows on one of my forums, but the rest are blank.
*note i have removed everything from the lastpostby template and only have $lastposter[userid]*

dont mind the theme, just something im finally bringing to life, but where i have circled their should be userids, topmost should be a 2 and the other missing one a 1 for my id.

*note 2* this way does work on the forumbit templates properly but i would much rather have it in the lastpostby template
so its a matter of what hook im assuming, and i've cycled through a majority of them and none seem to do it =/