Ehy,i just finished the companions storyline,then it said ask the companions leader for work.Point is,the three are nowhere to be found,not in Jorrvaskr,not in Ysgramor's tomb.Any clues?

How long ago was it yo finished Glory of he Dead? They walk all the way from Ysgramor back to Jorrvaskr, you know. If you have the quest active in your journal, you should see the arrows on them.
If that's not the case, I have no idea.

as said, they should pop up as quest markers when you activate the quest to talk to them for jobs

im not sure but i dont think theyre essential after doing their end quests anymore, so maybe they got killed somewhere if they dont show up

Sleep a couple of hours or wait a couple of hour (in game) then they should reappear in their stronghold in whiterun.