There's a few different situations where one might lose track of a companion. Most of these can be worked around with relative ease, but others practically beg for console assistance.
- While They Are Following You
- Companion gets distracted by "shiny thing" (runs off to fight enemy or pick up an item).
- Companion falls in combat.
- Companion is told to wait, and you forget where.
Without the console, these pretty much require one of three fixes:
- Brute-force search of the area.
- Run away and wait for them to catch up.
The first solution will, of course, always work. Eventually. As long as you're thorough and patient.
Running away or fast-traveling will certainly work for distracted or fallen companions, but I haven't tested it for companions who have been ordered to stay in a certain location. I expect that, in those cases, running away definitely won't work. Until I get a chance to test, I'd guess fast-traveling would probably work but won't guarantee it.
Also be aware that, for fallen companions, there is one more fix: Clear out the enemies in your immediate area, and wait for the companion to arise and return to you.
- While They Are Not Following You
- You dismiss a companion and subsequently cannot find them at the location you sent them to.
- You never actually pick up the companion after they've asked (or been asked) to join you for the first time.
- Random disappearances of idle companions.
These can really stretch your patience if you don't have the console because, well, you're playing on a console. (I play on Xbox One. So, if you want a PC console fix, you'll have to check @kalina's answer.) But they can generally be worked around. The first case is one that sent me Googling for an answer, and even then I didn't find the right answer for my situation (included as the last fix below). The latter is something I haven't personally encountered yet but, given the experience I had with solving the former, it seems very possible that it might happen.
Some solutions for this group are:
- Search the settlement you sent them to.
- For most cases, just running about and checking the common areas of the settlement will turn up your missing companion.
- For Dogmeat specifically, check inside or near any doghouses in the settlement. It's best if you just build one for him in a place that you'll remember.
- To help consolidate settlers and companions into one place, you could try using a bell. You may want to try moving the bell and re-trying it in multiple locations in the settlement - depending on how your settlement's structures are arranged, and where the resident NPCs are when you ring it, it's very possible that not everyone will find their way to the bell in every location.
- You could also try waiting until night time and doing a bed search. Not everyone will necessarily be in bed, but this still helps increase the probability that you'll be looking somewhere your companion actually is.
- In case you're mis-remembering a companion's assigned settlement, you might want to check your settlements' population counts in the Pip-Boy and go search all inhabited settlements.
- In case they might be "right in front of you, where you can't see them" try using VATS to highlight targets in the area. Keep in mind that "targets" refers to any NPC or creature, regardless of whether they're friendly or hostile, and any turrets. So this could get a bit noisy in highly-populated or well-defended settlements. Also, this won't work if the companion is actually following you at the time (hence why this isn't in the earlier section).
- Check their original residence.
- This question has a list of their locations, and a link to another guide.
- Companions will generally wait at their original residence if you don't choose to have them follow you immediately after gaining their companionship.
- There's also been some claims that a bug sometimes causes dismissed companions to go to their original residence instead of their assigned settlement.
- 1 and/or 2, plus waiting.
- Companions don't just instantly teleport anywhere under normal circumstances. (For a probable exception, see the next solution.) You might actually have to burn off some in-game time (wait/sleep) for them to get to wherever they're going before you'll be able to find them there.
- Go about your business.
- If a companion is supposed to be involved in the next step of a quest, and they're not actively following you, they may be found at the location of that next step. I had this happen with Piper recently. I dismissed her while I was in Sanctuary, and told her to stay in Sanctuary, and subsequently couldn't find her anywhere in a settlement or the Publick Occurences office. It wasn't until I picked up the main quest line again that I stumbled across her at the location of the next step.