Praying for him and your whole family. I know you'd be a worried man... very very worried, but my advice to you is to somehow manage to stay calm and do this -- it has helped me, my family members, and many friends and clients over many many years... so it may help you, and the readers too >>
Worrying doesn't help much during such stressed moments. At least one member of the family, you, should become calm and think -- visualize -- positively, and visualize without stressing out and without any doubt whatsoever attached, visualize that the child is safe and is returning home... that there are helpful people helping him come back safe and fast, that he arrives home -- as he used to do every other day. Just see (visualize) this and then release the thought (visualization) to God (which is ever present near you and him as a very positive energy field).
Be like a child while doing this visualization -- you know how children are, they know that their father will bring them the bat/ball/toy in the evening when he returns from office and they know that their wish in the morning has been granted by the most powerful person on this earth -- their father! Same way... be like that child!
With this type of visualization, you are creating vibrations to make things really happen. Please do not doubt this as it has really helped many... may it help you very positively and swiftly too. I know it WILL. God be with him, and you and your entire family. Amen!
God Bless!
And yes of course, do every thing else that's needed to bring him back safe and fast. It may help if you upload the missing message and his photo to FB... and request the readers to make it go viral -- to their friends and friends of those friends... Even 10 initial readers/friends can make it go viral all over England / NW England in no time. A photograph of your nephew will boost it. And then, a few of those 1000s will really begin to look for him and that would help the Police find him quickly. Give the related Police stn number and a contact number too, just in case.
P.S.:
Would he, by any chance, go to a relative / friend in Liverpool / Manchester / even Blackpool, or any other such place; or wanting to see some upcoming sports event in those places? Did he hinted about it (to your family member or even to one of his best friends) in any context in the last week before he went missing? (Just a persistent inkling here...).
Children would definitely tell one of the closest friends about what they want to do in such cases, and may be after he went missing the friend could have been extremely afraid to speak about it openly... you need to handle that particular situation about asking his friends very maturely.