I also doubt threats of imprisonment are likely to be a deterrent. Closing the border at Turkey would probably help stop the recruits from succeeding, but I don't see any real effort on Turkey's part to do this.
In addition to You Tube, Twitter, Tumbler, and Facebook, a big recruitment tool for foreign fighters is Ask FM, where individual fighters answer questions and describe their daily lives, and offer advice on how to get across the border. For personalized advice, they ask people to contact them on kik and offer to connect them with someone who can help with particular issues. Their tone is conversational, even breezy, and they show a sense of humor. One fighter, who also works in the media department, has answered more than 1,500 questions in the past month or so. It was easy reading, so I made a compilation of what I found to be the more interesting questions and answers in his thread. You can read it here.
They are well aware these communications are monitored, and don't seem to care. They don't hesitate to disclose who is in their group, which ISIS big shots they've met, how long they've been there, etc. They even answer questions about food and cooking, bathroom and laundry facilities.
There's a lot of women asking them questions about whether they want to get married, how a "sister" would go about it, etc. They answer some, but don't hesitate to remind them they aren't providing a dating service.
One of the best ways to learn about ISIS is to read them in their own words. Unfortunately, Twitter keeps deleting their accounts, including official ISIS accounts. ISIS moved its accounts another site, which also deleted them. A few weeks ago they moved to VK, a Russian owned Facebook lookalike. Today, VK zapped all the official accounts. That leaves Justpaste.it where they post photos and communiques, but it's not searchable, so unless you read on Twitter they've posted something new, there's no way to know. That's a huge mistake in my view. Analysts, researchers and journalists learn a lot from following them online. Governments could too.
In any event, until the Governments of the world start paying attention to why their youth are disaffected, marginalized and feeling oppressed, and make an effort to provide supportive programs and other assistance, they will just lose more and more of them to extremist groups. The State Department's latest effort, a video that tries to scare them off, is a waste of time and money and a losing proposition.