Click the Weakaura to cast your buff.
This clickable buff tracker will display the name of players missing your buff in your party/raid.
If more than 5 players are missing then the names will not show but the WA will glow instead.
Filters have been applied based on class as I couldn't be bothered doing it by spec. As a couple of examples: you won't see a Warrior is missing Arcane Intellect, but you will see a Balance Druid is missing Battle Shout.
The supported buffs are: Druid - Mark of the Wild, Evoker - Blessing of the Bronze, Mage - Arcane Intellect, Priest - Power Word: Fortitude, Warrior - Battle Shout