The 25-year-old man, from Wigan, is being held by Greater Manchester Police in connection with attacks on two men.
One, a 25-year-old from Skelmersdale in Lancashire, has been charged with attempting to meet a girl under 16 following grooming.
The other, 19, has been released on bail on suspicion of a similar offence.
Police said the first incident occurred at about 21:00 BST on Friday when the 19-year-old arranged to meet what he believed was a 14-year-old girl in a church car park in Atherton, near Wigan.
On his arrival he was filmed being attacked by a group of men who accused him of being a paedophile.
He escaped but later received messages demanding money and threats the footage would be uploaded to Facebook.
He reported the incident to the police on Saturday, was then arrested and subsequently bailed pending further inquiries.
Later that day, at about 14:40 BST, shoppers at Market Place in Wigan witnessed the Skelmersdale man being assaulted.
He also was accused by a group of arranging online a meeting with a 14-year-old girl. One of the men in the group attacked him, knocking out two of his teeth.
The episode was filmed by the group and has since been posted on the internet.
The man got away and reported the events to the police, who arrested him and charged him with grooming.

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"We looked through pinhole viewers and colanders. We also made a viewer out of a poster tube. We saw the sun turn into a tiny crescent and we got really chilly! It was amazing!"
Kestrels Class, Welford Sibbertoft and Sulby primary school, Northamptonshire

Charles Sirleaf was among 46 officials suspended for not making the disclosure to anti-corruption officials, it said.
He was one of three sons appointed to top posts by his mother following her re-election last year.
Critics accuse Mrs Sirleaf, a Nobel Peace laureate, of nepotism.
She has appointed her son, Fumba, as head of the National Security Agency and another son, Robert, as a senior adviser and chairman of the state-owned National Oil Company of Liberia (NOCAL).
Robert Sirleaf is suing two local newspapers - the Independent and The Analyst - and opposition politician Jefferson Kogie for libel for suggesting that he has benefited financially from the posts.
In a statement, Mrs Sirleaf's office said Charles Sirleaf and the other 45 officials would remain suspended until they declared their assets to the Anti-Corruption Commission.
Other suspended officials include the presidency's Chief of Protocol David Anderson, Solicitor-General and Deputy Minister of Justice Micah Wilkins Wright and Deputy Director General for Broadcasting Ledgerhood Rennie.
Mrs Sirleaf, who took power in 2005 at the end of 14 years of conflict, has repeatedly pledged to tackle corruption and to promote good governance in Liberia.
She was awarded the Nobel Peace Prize last year, shortly before she was elected for a second term in polls marred by allegations of widespread rigging.
Corruption remains a major obstacle to development in Liberia, where most people live in poverty despite the country being rich in mineral resources, analysts say.
A man has been arrested on suspicion of vigilante assaults and blackmail of men alleged to have tried to meet with underage girls, police said.
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Many parts of the UK have experienced a very rare partial solar eclipse, one of the most spectacular in years.
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Liberia's President Ellen Johnson Sirleaf has suspended one of her sons from the post of central bank deputy governor for failing to declare his assets, her office has said.