The first race of the second Chapter, Isle of Plight, is the easiest to get this one on since there are only 200 pedestrians. The way I did it was to first focus on wrecking 4 of my 5 opponents and damaging the 5th so I could search in relative peace and quiet. However even then the last few peds are tricky to find, but luckily there is a powerup that will show you where they are on the map.
It's in a red barrel above the large vertical concrete structure near the second checkpoint but you will need the Kangaroo on Command! ability to reach it. If you haven't found one in a random barrel, you can buy one from the menu (press left or right). It can be found under the Player then Control categories. This video (not mine) shows the exact location