2:18 pokeradar... Also dont run away from it oder the chain will break. (Go for the bushes that shine and look like water sprinklers) So just kill off pokemon till Du see a ditto. Whcih ditto's will keep poping up more. It took me 45 Minuten to find one so be patient.
Du Can find Ditto in Diamond on Route 218 but Du need the PokeRadar,to get the radar Du go to Professor Rowan after you've seen every Pokemon in the Sinnoh and Defeated the Elite Four ;)