While I would not be worried, there are many people (like your friends) that have eclipsed the 21 day wait time this year. I'm sure you will get the refund soon, but the IRS has been slower this year than in past tax seasons.
In case you do not know about this tool, you can check refund status here:
https://sa.www4.irs.gov/irfof/lang/en/irfofgetstatus.jsp