According to the Bangkok Post, Nsereko allegedly telephoned members of his family in Germany to claim he had been abducted in an attempt to extort ransom money.
Nsereko's family contacted the German embassy in Thailand, who investigated and helped to co-ordinate the arrest.
The 23-year-old will now return to Germany this week to stand trial for the charges.
Nsereko signed for the Hammers in January 2009 for a record fee in the region of £9m but struggled to adapt to life in the Premier League.
He made just ten appearances under Gianfranco Zola at Upton Park before returning to Serie A with Fiorentina.
The former German youth international has since enjoyed unsuccessful spells in Bulgaria and Italy and is currently contracted to German third division side SpVgg Unterhaching.