http://fallout.wikia.com/wiki/Recovering_missing_NPC_in_Fallout_3

Load a savegame where you still have your missing companion with you.

Open the console by hitting the tilde ` key.

Click on your companion. This will show his/her reference ID#.

Write that down somewhere.

Load the game where your companion is lost.

Open up the console again, and type without the quotes "prid referenceID", and substitute the reference ID number you wrote down for where it says "referenceID"

Type, again without the quotes "moveto player"

Your companion should magically appear near you.

Worked for me, hope it works for you.

In case it hasn't been considered why not just fast travel some place ? They seem to go through this same action of being moved to the players location. Been my work around so far.

Maybe a mod could copy this to the PC issues section as well.

In my case this was not a companion that was currently traveling with me, but one I sent to the Lucky 38 from some point in the wasteland. After a week of game time, that particular companion still had not showed up at the casino, and was basically lost to me. This helped me get him back!

In many cases during my own travels in the game, an NPC will get lost and will not fast travel with you. I'm not sure if he fell through the map or what, but this does get him back.

The problem with this, is it doesn't help with anyone playing on a console who has lost their companion/s.

Same. I lost ED-E somewhere in the wilderness when I told him to go back to Lucky 38. As far as I can tell, after that he just went *poof*

At present, I have all possible companions at the Lucky 38, but ED-E is nowhere to be found. I guess I will have to resort to the console to get him back.

i am on a console. i think the game is like FO3. if sidekicks get separated, they go to a designated spot after a certain length of time. i was at my motel room in novac, resting to pass time, and when i awoke, my side kick was there in the room with me.

On the Ps3 I know if any companion besides Ed-e goes missing you can go to vault 22 and use the elevator to go to oxygen supply. Works good for any of the not Ed-e peoples. I still haven't found my lost Ed-es.

or we could save a whole lot of time and just scan the map? there name and location pops up ya know.

also handy for those who use the consoles?

I like this one. ^

Wait for 7 game day and they will be in their original spot where where you hired them in the first place.
Or go to vault 22 in the lift and vol la they are in front of you.

Because that happened to me.

It doesn't work on the 360.