The crowdfunding campaigns where I have made contributions were shared directly with me via Facebook, or I noticed them in other people's news feeds with whom I share mutual friends, or they were emailed to me. The idea naturally lends itself to social media: whereas friends and family have traditionally been a source of financial support, now everyone else's friends and family can also potentially offer support. The ability to share these campaigns so prolifically creates a potentially infinite support network. Like a lot of other social media outlets, just visiting the website itself can lead one down the rabbit hole of personal requests, each one more compelling than the previous. The primary obstacle is probably the actual asking. I have read many campaigns that start similarly: "It is really hard for me to ask for help" or "I have always prided myself on being very self-reliant". I would imagine that like other authoring tools, crowdfunding websites offer tips and helpful suggestions on how to approach one's campaign ask.
One common function of crowdsourcing sites is a "ticker" of donors' names and contributions that updates itself as donations come in. There is usually an option to publish one's name or to remain anonymous. The ability to leave one's name off the list is a helpful feature if you are self-conscious about the amount of your donation. The social aspect implies that the campaign is semi-public and thus subject to the scrutiny of others, like so much of social media in which we participate today.