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!

No, this does in fact appear to be a bug with the McLaren.  If you don't take him down by the time he takes the second left hand turn, he disappears from the map entirely.  He does NOT appear on the larger map, he does not return.  He's just gone.  In fact, you can see him disappear if you follow him slowly.  The car is in front of you, but the black arrow icon used to show a Most Wanted car that needs to be taken down is gone.  You can even collide with the McClaren over and over and you will never actually take him down.

I'm using the PC version and have tried this race half a dozen times, beating the McLaren every time.  I've got every other Most Wanted car available to me.  But the McLaren is impossible to get.