Ms Hassle was last seen at around 1pm on Tuesday, September 21, at Perth College, University Highlands and Islands.
She has links to various places across Scotland – particularly the Dundee, Perth and Fife areas – and has been reported missing in the past.
Her family and friends are growing increasingly worried for her wellbeing and are appealing for her to let them know she is safe.
Ms Hassell has been described as white and 5ft 1in tall, she is slim built and has dark brown hair.
When she was last seen she was wearing a white shirt under a grey cropped top, with grey cycling shorts.
Constable Jack Stirling from Auchterarder Police Station said: “Mia’s family and friends are concerned about her wellbeing and are urging her to get in touch to confirm she is safe and well.
“She has gone missing before, and is known to have links all over Scotland, but particularly the Perth, Dundee and Fife areas. She has also spent time in various places in England.
“We are appealing for anyone who thinks they may have seen Mia, or has knowledge of her whereabouts, to please come forward.”
If you have any information you should contact Police Scotland on 101, quoting incident number 2069 of Tuesday, September 21.
Police Scotland has Missing Person Coordinators (MPCs) in every local division in the country.
MPCs support and oversee all missing person investigations.
Police Scotland says MPCs ensure missing persons have the “correct level of support” once they are found.