Andrew Rawson, who has written more than 40 books, said Pte Stephen Smith, lived at 6 Glave Street, off Coleridge Road, Attercliffe and died at the age of 23.
Mr Rawson said Pte Smith was killed in action at Suvla Bay on August 9, 1915, while serving with the 6thÂ York and Lancaster Regiment, leaving behind a widow '“Â Mrs S E Smith.
Pte Smith's medal was found by crews from the Yorkshire and the Humber Marine Unit while carrying out a search of the River Loxley in Hillsborough on behalf of South Yorkshire Police.
Sgt Paul Jackson, of the regional underwater team, said divers had found out Pte Smith served as part of the 6th Battalion York and Lancaster Regiment and landed in Gallipoli, in Turkey on July 2, 1915.
The officerÂ said the the team wereÂ desperate to reunite the medal with his family.
Sgt JacksonÂ said: 'We were on an operational job on behalf of South Yorkshire Police at the time and we were waiding through the water near Hillsborough stadium and doing a search.
'We were going slowly working our way down the river and one of the lads stopped because he thought he'd found a coin but then we realised it was a war medal.'
Mr Rawson said the 6th York and Lancaster Regiment were part of the 11th Division which formedÂ on August, 21 1914.
He said: 'After initial training at the regimental depots, the infantry battalions moved to Grantham in Lincolnshire.
'On June 12,Â 1915, the division received orders to prepare for service at Gallipoli and it embarked on theÂ AquitaniaÂ andÂ Empress of BritainÂ at Liverpool onÂ June 30.
'The division had sailed to Mudros by July 10. On August 6 and 7, 1915 the division landed near Lala Baba at Suvla Bay, in the hope of breaking the deadlock on the peninsular.'
The Star is calling for anyone with any information about Pte Smith or who knows his family to get in touch.
Anyone with any information should call The Star on 0114 2767676 or email [email protected] and we will pass on your details to the diving team.