Rule out the usual hiding places first. If the piece really is gone, check the set piece by piece
and leave with the element ID LEGO asks for, or a link to buy the part.
Cone 1 x 1 [No Top Groove]OrangePart 4589Element 4513993 or 4188454×1
Plate 2 x 4OrangePart 3020Element 4158355 or 4122468×1
Plate Special 1 x 2 with 1 Stud without Groove (Jumper)OrangePart 3794aElement 4189124 or 4159973×1
Technic Brick 1 x 1 with Pin HoleOrangePart 6541Element 6629202 or 4159975×2
Technic Brick 1 x 2 with Axle Hole Type 1 [+ Opening] and Bottom RidgesOrangePart 32064c×1
Tick each piece as you find it, or mark it missing.
When a piece really is missing
Ask LEGO
LEGO takes requests for pieces missing from a new set through its customer service site. The form asks for
the set number and each piece's element ID, the number printed beside the piece in the parts list at the back
of the instructions. This checker lists both.
Mark a piece missing and your list links it to an eBay search for that part, which also covers pieces from
older or second-hand sets.
Keep a record
Copy or download your missing list (the CSV opens in any spreadsheet), or print the whole checklist and tick
pieces off on paper. Your marks stay in this browser, so you can check a big set over several sittings.