I have won the race with MCLaren MP4-12c.But when I try to find him on the map,he does not appear.(I have to take him down)Usually they spawn as a black arrow can't find him at all pls help!

If u don't succeed to take down "most wanted" (after you beat him in a race)  , because   he escapes you  (disappear) ,then just drive around a little and in a minute he will  drive by (this will be repeated until you successfully crash him, so ,no worry  :D )      

+++ you can't see Most Wanted on a map (like you see him in a race)  , until he passes you ,so don't search for him ,cause he will find you :D :D :D