Those Quadrupeds can be very elusive.. You can force it move and hope it comes to the same route you are. The best I can offer is that you choose a Pokémon Center as your base, and Fly to it.
Choose a Route. Get in to a few wild battles, lets say 10 you've seen it by then. By now your Lead Pokémon is running out of PP. FLY BACK to your Base Pokémon Center, Heal. Head back out ON TO THE SAME ROUTE. Repeat. I recommend Vermilion and Route 11.
When you've seen it. You can Track it using the Pokédex's Area funtion.
I saw my Raikou on Route 14 (wasn't looking) and caught it on Route 9 (I was at in Vermilion when it was in Route 9, I just ran through Saffron and 2nd wild battle on Route 9: Traded Masterball away!).