How to track: Like the other trackable hunter pets, you will not be able to see him when he's up. He is completely stealthed. In order to locate him, you will need to find and follow his tracks - tracks that thankfully only hunters can see. Once you've found his tracks you'll need to follow them until you don't see any more. This is where I like to wait and watch where I think that he'll be walking next. Often times you'll see a new track appear right in front of you - this means you've found him!
Once you find him, the only way to see where he is, will be for him to walk through a flare. Don't throw your flare down on top of the track he just left, throw it a little further out in front of where you think he is. When he walks through your flare he will become visible. You can take this opportunity to tame, or you can throw a Hunter's Mark on him - which will keep him visible to you when he goes back into stealth. Hunter's Mark will make him visible to you, but only you when he's in stealth.
Glimmer's tracks are called "Flooded Tracks", and they really look nothing like any track you would expect to see from his weird bug feet. (I guess they're better than paw prints though.) His tracks are also not particularly difficult to find toward either end of his path. They are light in color on ground that is dark green through most of his path, making them stand out a bit. Like other beasts' tracks they do not stay up indefinitely; the furthest ones behind disappear one by one as new tracks are created.