There was one a few years ago I remember vividly as I was on it and reported it repeatedly and got the generic MN reply 'we have no reason to think the OP isn't genuine but don't give more than you can afford'. Which was the same message they posted on the thread.
Friday night. OP said she lived rurally with no transport. OP said her DPs wages hadn't been put into the account she had access to and when she texted him he said he'd left her and with no money. Her kids had only had breakfast that day as she was waiting for the money first thing and there was no food in the house but she'd been intending to walk a distance to the local shop to buy food once DPs wages were deposited.
No food banks as Friday night and all GP surgeries/social services closed. No family or friends she could call on as DH had been controlling and isolated her. No SM accounts where she could ask for help locally. No-one could drop food round even if they wanted to because she lived so rurally it wouldn't even come up on sat nav. And also, OP understandably wouldn't want to give her address to strangers on the Internet when alone in the house with DC.
Lots of 'I'm not asking for money, just advice' but the only possible solution seemed to be that someone put money in her account so she could walk to the local shop with all the hungry kids to buy food.
Lots of 'check your DMs OP'.
OP disappeared from the thread and ignored all the 'please update OP, we're worried and want to know you're okay' posts.
Next day someone posted on the thread saying they'd DM'd the OP and offered to transfer money which OP accepted and gave her bank details. And that poster had only sent £10 as that was all she could afford but the OP had a distinctive name and rural area so they'd looked her up on FB to see if she was on there and the OP had dozens of friends and lots of family on there so that poster felt duped and lied to.
A couple other posters then posted they'd sent £10 or £20 and were also angry they'd been duped.
Surprisingly, OP actually came back. Angry that someone had looked her up on FB and saying yes, a few people sent her money but she hadn't asked for it so it was up to them that they did and it was no-ones business why she hadn't asked any of her friends and family on FB to help her out.
Then thread was deleted as OP had 'privacy concerns'.
And yes, the MN Christmas present exchange ended because some people took from the scheme and didn't give back so it was abandoned.