You have to have an old pokemon GBA (gameboy) game to get it in diamond and platinum or you could trade someone for it.
growlithe is in route 36,37,48
I think it is only growlithe and arcinine.
Growlithe cannot learn Cut.
You can find a Growlithe in the Pokemon mansion. This is in FireRed only.
Growlithe cannot learn extremespeed.
Growlithe evolves into Arcanine using a Fire Stone.
Growlithe is only found in Heartgold Version.
you can catch a growlithe at route 37.
As far I know, there is no preevolved form of Growlithe. I think you must be mistaking it with Arcanine because Growlithe is the Arcanine's preevoled form and Growlithe only evolves if it is exposed to the Fire Stone.
Growlithe > fire stone > Arcanine
You have to use the Fire Stone on the Growlithe, not attach the stone to it. Growlithe evolves with exposure to the Stone.
Growlithe is one of the "version-specific" Pokemon. Growlithe is only available in HeartGold, while in SoulSilver you can only get Vulpix.