Katie Foulds, from Blackburn, was last seen close to Pleasure Island at around 4.15pm on Wednesday, February 10.
Police said her family and friends had not heard from her since and urged anyone with information to contact them immediately.
In an update released today (February 23), officers said they had obtained footage from a person who was flying a drone on St Annes beach on the day of her disappearance.
The footage they captured reportedly shows a “figure walking down the beach towards the water” close to South Promenade at around 4.27pm.
Although they “cannot be certain” it is the 22-year-old in the video, police “believe at this time” the figure is Katie.
“Although we can’t be certain that the footage is of Katie, taking into account the other lines of enquiry we have followed and the CCTV images around this time, both we and her family sadly believe it was her,” Det Insp Jamie Lillystone said.
“This is a desperately sad situation and our thoughts are with Katie’s family at this time.
Katie Foulds (pictured) is described as around 5ft 5in tall, with long brown hair and blonde highlights. (Credit: Lancashire Police)
“We would like to thank anyone who has assisted the investigation following the press appeals.”
Katie’s family have been made aware and are being supported by specially-trained officers.
The search for Katie continues and police are urging anybody who was on the beach at the time of her disappearance, or who may have captured any further footage, to come forward.
She was last seen wearing a brown-coloured ‘teddy’ jacket with black leggings, according to police.
Anybody with information can contact police by calling 101, quoting log 327 of February 12.