The dad, who wished not to be named to protect his daughter’s identity, said the attack happened last Thursday morning (January 6).
He said: “My daughter and her friend were walking back from the shops in Park Avenue when a man aged between 45 to 50 walked up to my daughter and punched her in the head.
“She fell to the ground covering her head, crying, terrified and in shock. The man stood there for a few seconds before running away.
“My daughter called me straight away and I drove straight back to the shops where the assault happened.
“I gave my daughter a big hug, she was crying and shaking. I put her in the car and walked into every shop that was open to see if they had CCTV for the outside, not one had so I checked a couple of houses that has CCTV which a couple had.
“I contacted the police again when we got home and within an hour a police officer came. She stayed for about 30 minutes and took a statement from my daughter.
“Afterwards I contacted 111 to ask for advise on my daughter and they advised me to take her to the hospital. We were seen by the doctor who examined her and found no bumps nor cuts.
“My daughter is traumatised and doesn’t understand why this has happened, she is not alone in this and I too do not know why this happened.”
A Sussex Police spokesman said: “Police are investigating a report of an assault on a teenage girl outside a shop in Park Avenue, Hastings, at around 8.45am on Thursday, January 6.
“The suspect is described as a white man, aged between 45 to 50, around 5ft 10ins tall and of muscular build.
“He had a long white beard with shaven hair on top and was wearing a black zip up jacket, blue jeans and white trainers with a blue tick on.
“Anyone with information which could help officers with their investigation is asked to report it online or call 101 quoting serial number 354 of 06/01.”