Opportunity sampling, snowball sampling and random sampling over the Net. Ways to gather a decent sample and publication options?

I conducted two surveys through a Facebook application. One of the topics were anonymity and aggression. The methods that i followed were a mixture of Opportunity sampling (post in fan pages and group walls etc.) and Snowball sampling (provided the users that took part in the survey at the end to invite their friends). Random sampling is really hard on Facebook due to people being reluctant to respond to pms that come from unknown(to them) people.

How easy is to publish a research were the sampling is not random? Do you know of any journals that do publish opportunity sampling research?