Do they even exist?
If someone tried making one on me id just laugh and walk away...
I haven't but my brother did one on a pick pocket once although he use to be in the Police so he had the training
What is a citizens arrest?
Basically don't bother: citizen's arrest is extremely dangerous. You are also liable to be sued under the tort of false imprisonment. Furthermore, if you falsely deprive somebody of their liberties ("arrest" them) then they can also legally use reasonably force to resist.
Basically you have to reasonably believe someone has committed or witness somebody committing an arrestable offence...
The police would really rather you wouldn't though, it's very dangerous both in terms of danger to your physical-self and in terms of your legal liability.
Basically it should be used as an absolute last resort where you know 100% that the person is responsible for committing an arrestible offence.
I think, bringing up my immense GCSE Law skills, a person can arrest and detain people who commit cartain serious ("arrestable") offences.
The reason no-one ever does it is because they can be easily sued if they get it wrong, unlike with a police officer.
I'm not even sure it's legally allowed. You'd probably get sued, or something.
I wouldn't risk it myself.
Don't want to be punched in the face whilst trying to enforce one.