Police say they would like to speak to the passenger in a car which was spotted near to where the fire was first sighted on Thursday, June 28.
Det Con Stuart Lunt, of Chorley CID, said: “This is a complex investigation and we are still working hard to find out how this fire started.
“If you recognise the man in the passenger seat or have any information which could help with our inquiries, please get in touch.”
Anyone with information is asked to call 101 quoting log ref 1176 of June 28.
Alternatively you can call the independent charity Crimestoppers anonymously on 0800 555 111 or you can do it online at www.lancashire.police.uk/reportonline