The 23-year-old singer said she was “terrified” after her pal was taken by a group of armed men.
The friend and another man, both in their 20s, were working at a sports store in west London last month when the men apparently entered the store and bundled the shop workers into a car.
The group are alleged to have held the pair hostage at an address in Thamesmead, south east London, and demanded a ransom of £75,000 from their families.
Lily’s friend and his co-worker were found by police a week later on August 9. They were handcuffed with their heads covered but were unhurt.
A number of men have appeared in court in connection with the alleged kidnapping.
Allen wrote on her blog: “Thank you to the Met for getting my friend back, we were all terrified and from what I hear you guys did an amazing job.”