The attempted robbery happened on the Cross City Line between Shenstone near Lichfield and Butlers Lane Railway Station, in Four Oaks.
British Transport Police said the victim was approached by the group when then attacked him.
An investigation has been launched and the officers are hoping to hear from any witnesses who may have information that could help find those responsible.
The incident happened at around 1.30pm on March 17.
Anyone with information should text 61016, or calling 0800 40 50 40 quoting reference number 2300030529.
The Cross City Line runs between Lichfield and Redditch via Birmingham New Street.