How to inform/attract more candidates for a postdoctoral position? When having fund for hiring postdoctoral fellow, it is tricky to find highly qualified applicants, since they can get aware of the opening position by chance. For almost any postdoctoral position (it should apply for any position, but more severe for post-doc), there are better candidates who were also interested, but did not hear about the opening.

Possible approaches are not very effective.


Spreading by word of mouth through colleagues is very limited.
A few applicants may browse research group websites for checking
opening positions. Moreover, search engines do not index and rank
them quickly to reach the deadline.
Posting on academic job websites is good, but most of them are paid
websites. For faculty positions, universities have enough fund to pay
for advertisement, but it is difficult to cover the advertisement cost
by the limited fund of a postdoctoral position.
Free job websites are not very common for academic positions.


How to find more effective ways to inform and encourage more potentials candidates to apply for a postdoctoral positions to have a better chance to select a highly qualified applicant?
Possible outlets I can think of include:


Field-specific e-mail lists
Department email-list forwarded through collegues at other departments
Adverts inserted in talks/presentations held by people at your department (e.g. at invited talks, conferences etc.)
Job ad websites (national and global)
Advert at research-focused web communities/forums, such as Researchgate and Academia.edu, as well as LinkedIn.