It should be avoided everywhere. I've noted that it's common on this site (or used to be) among Arabic speakers from north Africa. But it's not correct English usage. "Hi, Dear" - with a capital 'D' because it's a substitute name, like 'Dad' or 'Honey', is only used for intimates. 'Dears' is very uncommon.
Should "Hi, dear/dears" be avoided in polite circles?