A financial planner has been arrested for deceiving six elderly people out of $700,000 with investment schemes that did not exist, South Australian police say.

The 80-year-old man from the Fleurieu Peninsula has been charged with 16 counts of aggravated deception and three counts of deception.

Police will allege the victims handed the money over for investment schemes for their retirement, but the suspect used the money for other purposes.

The stolen funds have not been recovered.

The offences were allegedly committed between 2005 and 2017 when the man was employed as a financial planner. 

Detectives are yet to determine whether there are any more victims or offences against the man.

The man was bailed to appear in the Victor Harbor Magistrates Court in August. 

Police are warning the community to be cautious about investment opportunities online and on social media, which scammers used to lure potential victims to fake websites.

Police warn people to be suspicious of individuals who pressed potential victims to act and make financial decisions quickly.