How do you catch plusle in heart gold and soul silver?

Answer 1

You can find one on:

Route 1, Route 2, Route 3, Route 4, Route 5, Route 7, Route 8,

Route 11, Route 14, Route 15, Route 16, Route 17, Route 18,

Route 29, Route 33, Route 37, Route 36, Route 37, Route 38, Route 39,

Route 46, Route 48, National Park

I suggest using a pokemon that is a higher level to almost knock it out.

Or you could just use a very powerful ball (ultra ball, nest ball).