Lost Freshwater Shrimp?

They are capable of eating them, if the shrimps are small enough.

I would hunt around the tank, make sure the shrimps are not holed up somewhere.
If you can't find them, then i suppose there is only one conclusion.

Thanks guys x
will have a look round, any suggestions as to possible hiding spaces ?

Depends what you have in your tank.

Plastic ornaments they like to climb inside where it's dark, same if you have wood or other cave like structures.  Small spaces between plants, under leaves, base of stalks.  They can be in many nooks and crannys.  I have 9 Amano's in my 180L, and I see maybe 3 or 4 at a time... can't see any right now.

Good luck finding them.