The former couple ended their marriage in December when Brand, 36, filed for divorce due to "irreconcilable differences", reported Contactmusic.
"Katy's been trying to get him back! She's a lost soul right now," a source said.
Perry, who married Brand in a traditional Hindu ceremony in India in 2010, is said to be missing him after she visited the country earlier this month to perform at the opening ceremony of IPL.
"She'd already been missing Russell. Being back there stirred up even more old feelings," the source added.
After their split, Brand has been romantically linked to model Nikolett Barabas while Perry is said to be dating Baptiste Giabiconi.