Pokémon GO launched with the ability to track wild Pokémon, but it proved to be glitchy and developer Niantic later removed it. Since then, they've been testing out a new tracking feature (called the Nearby Pokémon feature) in beta form in select regions, and over the past few weeks they've steadily been adding support for more regions. If you live in the United States or Europe and you're still lacking the ability to track, that could be changing soon.
The biggest rollout yet is in progress now, as Niantic has just announced that they're expanding the feature " to the rest of the continental United States and large parts of Europe." Niantic did not specify which European countries will be receiving the new tracker, but we'll be on the lookout for updates as it becomes available in more regions.