tweeters

There is a power curve in the audio frequencies.  As the frequency goes higher, the need for power goes down.  By the time you get to the operational range of a tweeter, the need is miniscule...a watt, maybe, with some power left on tap at the amp.

But while that tweeter needs something to make it tweet, at the same time other bigger drivers are demanding their share of power for their tasks.  As ianarian said, use the components' power ratings as a guide.  And always be sure to use crossovers; they will be supplied in a multi-driver arrangement in one way or another.