some ideas to modder who may be able to work on it
as first and easier part of the kidnapping i believe could be done if the modder use the "teen run away" or "sneak out at night" interraction which make them "leave the lot" and maybe combinate this with the parents pick up child visitor (which happen if ask a child to join the group, they keep following instead of going home) at late time a parent or adult of the child household will come to pick him/her up
is default (i
think since appartment life) but im not sure when this was introduced
this could be used as the kidnapper, just my suggestion on how it could be
also can take look at the pet run away interraction which let us use the phone and report missing pet
the pet will be unclickable, but still appears on the family side bar, after long time it might happen a random sim brings the pet back to family
maybe can be set trigger on a sim aswell SimPE is mighty
wish i would know how it works