The incident took place at the Greenfields Traveller site in Braybrooke on July 10 last year and left the teenager with life-changing injuries.
So far 16 people have been arrested as part of the investigation.
Fifteen people have been arrested on suspicion of attempted murder, with the 16th arrested on suspicion of being in possession with intent to supply Class A drugs.
All 16 have been released on bail pending further inquiries.
Now police want to identify seven men spotted in The Wheatsheaf pub in Peterborough on the day of the shooting.
Det Insp Lee McBride, from the Organised Crime and Drugs Team, said: “This was a very serious incident which has left the young victim with life-changing injuries.
“We have conducted extensive inquiries as part of the investigation and are now asking for the public’s help in identifying the men pictured.
“We believe they may be able to assist us with our inquiries and are urging them, or anyone who may know who they are, to call us on 101 or independent charity Crimestoppers anonymously on 0800 555111.”
It is thought the men may have links to Cambridgeshire, Leicestershire, Hertfordshire, Bedfordshire and the Thames Valley region.