The X Factor USA judge is said to have met up with the former fiancée of F1 driver Jenson Button several times, reports The Sun.
A close friend of Cowell said: "She and Simon have started to get very close.
"It is early days but there is certainly a chemistry between them."
Griffiths, 34, was also invited to Cowell's Beverly Hills mansion for his 53rd birthday celebrations.
The model started dating Jenson Button in 2000, and were set to get married in 2005 before it was called off just three months before.
The friend added: "She knows there are commitment issues [with Cowell].
"Currently this is not serious but the beginnings of a promising relationship."
Louise Griffiths was previously in the girl group Orchid, who originally recorded Girls Aloud's 'Sound of the Underground'.
She later appeared in the second series of Fame Academy, reaching the final eight. She has more recently turned to acting, appearing in the Tekken movie and an episode of NCIS among others.
The actress also dated House star Jesse Spencer from 2008 to 2010.