PMCF Survey Recruitment

What are some strategies others have used to recruit a reliable sample to participate in PMCF surveys. We currently use a convenience sample and promote the surveys via social media to reach end users. The idea of an email blast out to those who have provided it for ordering purposes has been discussed (our online privacy policy permits the use of email for business purposes) but there is hesitancy as we don't want to irritate our customer base. I was just wondering what other strategies may be deployed. Thanks!