For PC:
F1 - Target this enemy. I've had a few games where team members would target the stealth characters which has saved my hide on several occasions. I've started doing the same thing, but as soon as one person gets the attention of the other enemies, they stealth, so you've got to be fairly quick to target. Another indicator for the stalkers is fire. Nothing like an invisible enemy set on fire to make them obvious, except they don't always seem to destealth when this happens. It's funny, nonetheless, I've seen people get shanked by them, walking ball of fire and all.
F2 - Fall back. The lines on some characters are rather ambiguous, I find it better to use F4 for getting everyone's attention as it has the shield pop up with the red outline.
F3 - Thanks. Sometimes, it sounds more like a "Good job" than a "Thanks", but that's just me being pedantic.
F4 - Come here. You know that call that people spam whenever they find a class door they can't open? Yeah, this is the one. It's the best attention grabber there is, save for using your microphone.
I've been shanked by stealthed enemies more times than I care to admit, but if you're aware when the team is about to descend upon a spawn of enemies, taking out the stalker or highlighting him is a good strategy. I frequently play the Archer kit, and my targets are primarily the enemies archers, stalkers and lines of enemies just asking for a long shot to skewer through them. The tank can't do their job if they are killed by the firing squad before they get to the heavy hitters, that's probably why I don't enjoy playing tanks, because I can't play them worth a damn and enemy archers are the bane of my existence when I play melee kits.