Seven-year-old Julian Cadman is missing in Barcelona after Friday morning's terror attacks, his family say.
Family and friends of Julian are sharing photographs of the little boy widely across social media in the hope he will be found alive.
At least 13 people were killed and more than 100 injured in the terror attack on Barcelona's Las Ramblas on Thursday.
Jom Cadman, Julian's mother, was found in hospital and is in a serious but stable condition. Her son has yet to be found.
Julian's cousin, George Cadman, wrote on Facebook: "My cousin, Julian Alessandro Cadman is missing. Please like and share.
"We have found Jom (his Mum, my cousin-in-law) and she is in a serious but stable condition in hospital.
"Julian is 7 years old and was out with Jom when they were separated, due to the recent terrorist activity.
"Please share, especially if you have family or friends in Barcelona. Thank you."
The boy's aunt, Claire O'Sullivan, and his grandfather Tony Cadman, from Sydney, also posted similar pleas.
His distraught aunt Maricar Querimit Estera said his "family were waiting for him."
"My nephew is still missing ... they need help to find him quickly ... pls share," she posted on Facebook.
Another family friend, Sarah Auzner, pleaded with the public to share his photo.
"Please, please share his picture so he can be with his family," Ms Auzner wrote.
"We are beside ourselves with worry. Andrew and Jome Cadman we are praying for you."
Foreign Affairs Minister Julie Bishop confirmed that four Australians had been hurt in the attack, while one person is missing.
The Department of Foreign Affairs and Trade has been contacted for comment.
With Telegraph, London
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