The fire followed a large party held at a holiday cottage at Kilgram Farm in Jervaulx in the early hours of Sunday 9 September 2018.
Two men were seen talking between a Dutch barn and a barn containing livestock. The men were shouted at by the owner of barns to move.
Officers are appealing to these two men to come forward as they could have important information that could assist the investigation.
If you are the two men or know who they were, please contact North Yorkshire Police on 101, select option 2 and ask for PC Michaela Godridge or email Michaela.Godridge@northyorkshire.pnn.police.uk
If you wish to remain anonymous, you can pass information to Crimestoppers on 0800 555 111.
Please quote reference 12180168645 when passing on information.
The fire destroyed around £8,000 worth of hay. Thankfully, the pigs in the adjoining barn were safely removed before the fire took hold.