Urgh, what a thread!
I thought I'd lost DS1 forever when he was 11. A friend had invited him and a bunch of others to go swimming one morning in the holidays, and at lunchtime the friend's mum had rung to ask if he could stick around for the afternoon for a barbecue on nearby downland. I knew roughly where they'd be and she said she'd bring him home by 4. OK, fine.
4 came and went. Well, ok, things run on sometimes. 5 came and went and I'm starting to worry a bit. Unfortunately the mum's mobile is on the fritz and the landline she rang me from at lunchtime is going unanswered, which makes me think they're still on the downs or on their way. By 6, I'm really not feeling laidback anymore. Still no answer on the landline, so I decide to drive up to where I think they'll be on the downs.
No sign of them on the downs but there's a rural business nearby where some blokes are just packing up for the day so I ask if they've seen a bunch of kids having a barbecue. Nope, no one's been there all day, they say, which seems odd. Meanwhile, still no answer on friend's landline, and DP (at home) confirms DS still hasn't arrived. So next I drive to the friend's house to see if they went home to hang out instead. But no, no one at friend's house. Still no sign of DS at our house. So now I start ringing round other parents to see if anyone else's kid is on this outing and if they know anything.
Just at this point, standing outside the friend's house, I happen to see the big transit van that belongs to the rural business out on the edge of the downland driving though town. In a moment of inspired but completely irrational paranoia, I decide that DS - and possibly all his friends - have been kidnapped by the guys in the van, who are probably at this very moment on their way to the ferry to traffic them into sexual slavery in mainland Europe. May have seen too many lurid TV dramas.
I'm not sure if I'm proud or ashamed of the fact that I made a split second decision to jump in my car and 'follow that van', but I did exactly that, did some very nifty tailing and lane changing, though I say so myself, and followed two extremely bemused guys to... Tesco. 
Fortunately, just as I was about to confront them and demand that they open their van up for inspection, DP rang to say that DS had just been dropped off by apologetic friend's mum three hours late.
Bought him a mobile after that.