@Samuella,
Quote:Is it right to use - 'Who's my pen?' in lieu of 'Who has my pen?'.
No.
In this and similar phrases, it's much more common to use "got", especially in a colloquial context.
e.g. "Who's got my pen?"
Use "instead of" or "in place of" in informal writing, instead of "in lieu of". Your meaning is clear, but it's not a common phrase.