I once lost my bitcoin to an investment platform and it took a while before I managed to get my bitcoin back. My question is I want to know how many people have lost their bitcoin and how do you manage to get them back?.
How to you recover a stolen bitcoin lost to an investment scam?
how do you manage to get them back?
Generally you don't.
Take MtGox as an example. It is believed that a very large amount of money was stolen. so far as I know, none of that has been recovered. A small amount was discovered that the MtGox staff had lost track of and last I heard this was to be returned to the customers. If so some customers recovered some of their money. This was only possible because the exchange was based in a country relatively free of corruption where administrators were appointed and there was a police investigation.
Another example would be Quadriga-CX where the owner either died or faked their death and was the only person who had access to the private keys. So far as I know no customers got any money back.
These were initially genuine businesses and probably not investment scams from the outset. They were large exchanges with many customers who lost money. For smaller exchanges in countries where law enforcement is poor, there is even less chance of recovering stolen funds.
There are probably large numbers of people who gave money to scammers who created a website that was only around for a few months before the scammers moved on and set up new ones. Those victims are very unlikely to have the resources to do anything and even if informed police will likely feel the amounts are too small to warrant spending time on them. In a dispute over returns on a speculative or failed investment it might not be obvious that there is evidence of a crime. Some events may be disputed and may fall under civil law (e.g. contract dispute) rather than criminal law (e.g. fraud)
I want to know how many people have lost their bitcoin
Nobody knows. No-one tracks this globally. Not everyone reports loss to the police. Local police might have data and might report it nationally but they often might not know if the claims are accurate. So at best, some countries will have an estimate of total cryptocurrency crime but they might not break the figures down in the way you might want.
People also lose money for reasons other than fraud. They don't make backups then lose their computer or phone, they forget they had a wallet or an account or forget the password. Sadly people die and their family often are unable to find their keys even if they know their dead family member had Bitcoin.
You can't know how many people have lost their Bitcoin because bitcoin is not lost. If you have your private keys, you have the Bitcoin, so the Bitcoin change from one hand to another hand (EG. if you send your Bitcoin from your wallet to another person).
The problem with most platforms is that they are in control of keys, this means that they have the Bitcoin, not the person that are investing.
And the only way that you have to get them back is taking back control of the private keys.