In court documents, police say the alleged victim exchanged messages last Thursday with a "squirt.org" user who used the name "youngboihorny" and pretended to be 15.

The 61-year-old man claims that while he thought he was being "set up", he agreed to a meeting in Hawker to expose whoever was behind the account.

When he turned up, police say a 16-year-old boy and Lachlan Robert Wilson, 18, threatened him with a steak knife.

The pair then allegedly forced the man to withdraw $100 from an ATM, leaving him with just $17 in his account.

The teenagers are also accused of stealing a bottle opener from his car and telling the man they would contact him within a week to collect a further $200, or else expose him as "a paedophile".

The man went to police on Friday, and an AFP covert operative later contacted Mr Wilson using the man's phone and asked: "How can I make this go away?"

In response, Mr Wilson allegedly wrote: "It won't be going away for a long time unless I get a fare share of money. I know your name, address, ur car details, and videos of you grooming children. A good idea would be to sell your valuables. Block me and I'm going to the police simple [sic]!"

Mr Wilson is said to have gone on to write that the man could regularly pay $200 or fork out "one big lump sum to be left alone for good".

Police subsequently arrested Mr Wilson at a Narrabundah hotel on Saturday morning, before taking the 16-year-old boy into custody at his Hawker home that afternoon.

The teenagers have since been charged with aggravated robbery and blackmail.

When Mr Wilson appeared in the ACT Magistrates Court on Monday morning, he was refused bail.

Magistrate Robert Cook said he was concerned about the sophisticated method of alleged offending, and that he believed there was a risk Mr Wilson might interfere with witnesses or evidence.

The 16-year-old boy, who cannot be named because he is underage, fronted the ACT Children's Court via audio-visual link from the Bimberi Youth Justice Centre a short time later.

His lawyer, James Maher, said the Year 11 student had been "led astray" recently by Mr Wilson, who was "the driver of this enterprise".

Mr Maher acknowledged the seriousness of the charges, but said the allegations suggested "vigilantism", perhaps initially well-intentioned, might have played some role in motivating the boy.

He proposed a series of strict bail conditions, including a nightly curfew, significant restrictions on mobile phone and internet use, and prohibitions on contacting or being within 100 metres of Mr Wilson and the alleged victim.

Upon hearing the proposals, prosecutor Madison Fieldus told Mr Cook she would withdraw her opposition to bail if the magistrate was minded to impose the conditions.

Mr Cook agreed to do so, but warned the boy that any breaches could land him back in youth detention.

The boy is due back in court later this month, while Mr Wilson is scheduled to appear again in December.

Neither of the defendants have entered pleas.

Detective Inspector Matt Reynolds, of ACT Policing, said in a statement on Monday that intimidating someone for property and cash was "disgraceful and unacceptable".

"Sadly, with more people using online dating sites and online applications, some people have decided to use those services to manipulate, threaten or rob others," he said.

"As with any online service, people need to remember they may be dealing with someone using the internet to take advantage of others.

"When arranging to meet someone through one of these sites, people should act carefully to make sure that first meeting is in a safe place."