From the experts:
Piers was the first version of Peter to reach the English-speaking world, via the Normans, but it's never made it in the US, despite its large measure of understated panache. This might change due to the high visibility of TV personality and former news editor Piers Morgan.
There's a famous satirical medieval poem called Piers Plowman, in which the title character symbolizes the virtues of honesty and industry. Piers Whiteoak is a main character in the sixteen-book series Jalna by Canadian author Mazo de la Roche; Piers Polkiss is the best friend of Harry's cousin Dudley in the Harry Potter books.
The surname form of the name, Pierce, is better known in the U.S., partly via actor Pierce Brosnan.