The major problem in the use of social network in learning is trust. When there is no reference to source. The information lacks evidence to convince the learner. However trust can be established with citations or references to give the learner confidence to use this knowledge.
It's interesting that you've brought this up considering that the MLA has come up with a standard for citing Tweets from Twitter (http://www.mla.org/style/style_faq/mlastyle_cite_a_tweet). I also found out that Boise State has put up gudelines for Twitter and Facebook as well:
MLA requires that any electronic source is citing as a Web Publication. Make sure to include Web in the citation.
Include this information:
Editor, screen name, author, or compiler name (if available). “Posting Title.”Name of Site. Version number (if available). Name of institution/organization affiliated with the site (sponsor or publisher). Medium of publication. Date of access.
Use the date accessed for older MLA style and do not use the date accessed for new MLA style.
Examples for Twitter:
Twitter handle (Author). Web log post. Twitter.com. Date posted. Web. Date accessed.
When using social networks / media in learning, are you experiecing learners not trusting the source (which I find odd these days as many high-school and early university students often use Wikipedia as sources), or is it that the instructor not trusting the source? I do find that trying to cite something from Facebook is problematic as you don't have a definitive URL to go back to and depending on privacy settings you may not be able to actually have students (and peers) be able to go to the source itself.
In all things however, if you are using social networks and media as sources, you always need to consider who the actual source is coming from. i.e. Hawking123 may not be creditable unless you know that it's actually Stephen Hawking providing advice, comments or being quoted. There is usually a source reference (i.e. who said it), but verifying that it is a credible source is the most difficult part; Google and Twitter make great efforts to ensure that someone who is using a famous person's name is who they say they are, for other social networks it may not be clear cut.
I find your response very educating, however am aware that using the URL for referencing is alright. The issue on trust comes when the writer does not make reference or cite the source of the information so that readers can also go to the source if they wish in order to be assured of the credibility.
I see, in these cases it's troublesome especially when the writer is commenting something that you wish to verify. Its the difference between verifiable claim and opinion. Former president Ronald Reagan's catch phrase was "Trust, but verify" which is especially important in this day an age; a writer can't be creditable unless s/he can back up their position with facts.
Sometimes the source is creditable based on reputation i.e. if a notable scholar is providing an opinion or conveying a message, the learner based on who is providing the information may be more apt to believe it. But if you're going to quote or use it as a source for an additional work, you're going to need more verifiable proof.
I am very intrigued by your question. It can be extremely hard to trust what is out on the internet, especially on Twitter. With user run sites like Twitter and facebook, half of the things posted are opinions. Some may not be presented as such, which is where the problem lies. When I was in high school, wikipedia was an example of a website that could not be used as a reference, because it is also a user run site. I think that it is really important to know your audience as well. If you are in a high school where the students have a better understanding of what is true and what isn't, then you may be a little safer in comparison to an elementary school, where the kids may or may not know what they are reading.
Another possibility would be for your students to get the idea from a social network and then maybe do some outside research based on the initial idea. This could be a good opportunity for some extended research projects. In response to Angus, I find your post very educational and interesting. I had NO IDEA that the MLA now cites twitter.