You can not
You have to send the pet to attack before the stealth is cast.
If you do that, yes the pet will continue to go and knock the rogue out of stealth.
That is by design, see the updates thread.
But, you can not send pet after the fact.
Even if you know i stealthed, and you know i was in or around the farm house, after i stealthed, unless you can make me become seen, like say flares or goggles etc, you can not pick me to send pet after.
If you are persistent, you can run around and keep trying to target me for when i come out of stealth, if i decide to actually stay in the vicinity of a mad flare flinging hunter and his pet, but i probably wont choose to do that.
Another thing, lets say i am behind a wall
You are 50 yards away.
For giggles i pop stealth (prowl for me)
Ok so you get this alert right? You see my name.
It is too late at that moment to click my name to target me, you will have to find me unstealthed
Now, your maps pings, except it does not ping my location, it pings where you are standing.
Now, you dont know if i am behind the wall 50 yards away, i am behind the little barrel 4 yards away, i am behind the hay stack 100 yards away, or i am watching you from the window of the barn 200 yards away.
You only know i am someplace within a 200 yard circle of you, i could be right behind you, or i could be far away and not even bothering with you.
All you really know for certain is that i stealthed, and i am not your faction, where it goes from there is up for grabs.
In fairness, if i stealth 4 yards away behind a beer barrel, and you dont see the big bright giant enemy health bar poking around the barrel, you were probably meeting a bad end soon anyways
Plot error, needs editing.
If our hero stealths and THEN goes out into the world in search of the wicked Gnome, the Gnomes spy will fail to warn of anything, and the movie will end prematurely with the Gnome getting ganked, does not make for good climatic ending battle