Clearly, despite faculty and student diversity, this is still going to a fairly defined 'university population' rather than the wider general public.
There are several ways of getting your survey (or requests for participants) under the eyeballs of more people and they'll have varying degrees of success. I've never tried to do this myself but my top-of-head suggestions might include the suggestions below, but here's my main question.
Is there a website / database to which students can add details of their survey, perhaps categorised by topic and type of help wanted?
It sounds like the sort of thing people like MySociety might build, or a few enterprising university-based nerds. Possibly JISC might help. Maybe not.
I'm thinking of something that would be available for any student at any UK university, so it would need some buy-in from all UK unis. It would - in my fantasy world - be promoted by all public engagement / outreach officers at events and on websites, and members of the public would be able to help out on a student's research project. Possibly people could sign up or get RSS feeds telling them when something to do with a particular topic becomes available. Where appropriate students could post results arising from their work and what this has added to our knowledge of a topic, or validity of a new method etc.
Aeons ago I signed up to Focus Force which lets people hear about focus groups happening for various things. That's a commercial venture but I'm sure something similar could be organised without great cost and it would seem to benefit an awful lot of people in universities.
UCL has a scheme in place for people who want to take part in its lab experiments, possibly other universities have other arrangements - it just seems odd that surveys especially (online, one's location is likely irrelevant unless the survey is about 'living in Bristol') can't get a wider audience.
Anyway here are my suggestions - it's entirely possible they're crap, as I say I don't run surveys and don't recruit anyone to them.
Facebook - ask your friends to do the survey, ask them to share it. You can even pay to promote it to a particular demographic if you wish. Obviously if it's just your friends then there's another risk of biased results.
Post your link more than once a few hours or day(s) apart but intersperse it with other things too. You can also tag a few people and ask them to help out but don't spam people.
Twitter - obviously. Great way to reach people. Best to spend a bit of time getting to know it first though. If you want to reach a particular target audience it's wise to spend some time searching, by keyword, for accounts that talk about what you're interested. See who they're following, see what hashtags they're using, get to know them. Twitter's more about building relationships than spamming people.
I recommend posting the link a few times at different times of day and on different times of day. Make sure you post other things in the interim otherwise your portfolio of tweets will look spammy and dull.
Hopefully other people will retweet your request, here are examples of where I've done that:
Ppl who like London, pedometers, kittens, smartphones &helping UCL students get data might also like the Fitbit study http://t.co/Xh8FSHShsM
— Jo Brodie (@JoBrodie) April 22, 2013
Got headphones? A kindly disposition? ~10-20min? Combine the 3 of them &help out an MSc student doing audio research :) http://t.co/eX0m9RMg
— Jo Brodie (@JoBrodie) January 11, 2012
Newsagents' windows / supermarket community boards - in among the ads offering a child's bike and three piece suite why not add your request.
Gumtree - do people ever use the site for that sort of thing? It seems to get used for everything else so sounds like it might be worth investigating but I've never used it.
Create a mini site - you can create a really nice free website on Wordpress or even here on Blogger and put up a bit of information about your research, how people can help by taking part and a link to your survey. You can add new bits of information about it but it might be a lot of work for very little return.
Here's an example though by a student at UCL http://www.dbpharrison.com/general/walkerbitrecruitment/