I do this and it happens...

[DontEatRawHagis]

My Ranger and Rogue players have abilities that say there is no roll invovled. The Thief's background grants them the ability to locate local Thieves(this may just be a beta ability I allowed to carry over).

The Ranger has a tracking ability though that doesn't allow me to say you lose the trail.

Is this true? Or is there something I'm missing?

[Fwiffo86]

My Ranger and Rogue players have abilities that say there is no roll invovled. The Thief's background grants them the ability to locate local Thieves(this may just be a beta ability I allowed to carry over).

The Ranger has a tracking ability though that doesn't allow me to say you lose the trail.

Is this true? Or is there something I'm missing?

Tracking requires Perception and Intelligence rolls.

I would assume the same for locating local thieves. He knows where to look for them. Doesn't mean he automatically finds them.

Do you have the PHB or are you operating off the test packet/basic rules?

[FadeAssassin]

My Ranger and Rogue players have abilities that say there is no roll invovled. The Thief's background grants them the ability to locate local Thieves(this may just be a beta ability I allowed to carry over).

The Ranger has a tracking ability though that doesn't allow me to say you lose the trail.

Is this true? Or is there something I'm missing?

The thief background gives you a criminal contact. You know how to contact them and such, but the information will take some time to get to them and for them to get back to you.

Rangers get Advantage on Survival Checks to track their favored enemies, and can learn the exact number, sizes and how long ago they passed through the area.

EDIT: If you're using Playtest Rules then the ranger thing is by the rules correct. But I would seriously suggest to convert to the official edition. It just makes the most sense. The Playtest was just that, a playtest, so there is bound to be features that are OP. (not that there couldn't be OP features in the full game)