When looking to optimise candidate conversion from social media the question you need to ask is "Why are potential candidates not applying?" - i.e why do you have drop off in your process. Before anyone shouts out, lets make things real, unlike retail, in recruitment we do want an amount of drop off it is candidates self filtering themselves for roles.
I am not a social recruiting expert, but I am used to analysing conversion funnels. If your conversion experience can not be completed on a mobile I can say for certain that you are suffering enormous drop off just because you have not provided your candidates a mobile option. Given the high intensity of social media and email consumption on mobile devices, which is growing every day, this should be a priority for you.
The mobile application will take time to get right for your back office process. It might require some changes if you want to maximize the potential talent in your audience, or some investment with solutions such as Jibe or Mobolt. The traffic the numbers make it worthwhile. Support mobile properly and you will significantly increase the ROI you get from social media campaigns.
There are various ways to approach improving your process and perfecting your application funnel (conversion funnel). In various projects I have worked on the typical approach is to A/B test. This is a tactic where a % of your Internet traffic randomly is direction to the original user experience (version A) and the rest is directed to your new experience (version B). Using this approach and careful small changes it is possible to learn (and prove) exactly what changes deliver increased value. Many of the major .coms use this approach.
The ins and outs of recruiting have many details parameters that could impact your tests. It takes a lot of effort to plan solid A/B tests and knowledge, plus experience to correctly interpet the results. For the majority of recruiters I would suggest a different approach where by you use mobile optimise various recruiting campaigns. Your experience in recruiting will instinctually give you a feel as for the impact. Observing social conversions for the mobile campaign compared to none mobile campaigns will provide you data to back up your instincts.
Adopting mobile campaigns coupled with your social campaigns enables you to have a strategy to develop the perfect mobile engagement for your companies and candidates needs. You will be able to experiment with campaigns using high levels of graphics or video compared to text only. You can learn if supporting content on your mobile campaign increases conversion or if pure job adverts is the way forwards.
What ever your plans - supporting your campaigns with mobile targeted sites will expose you to more candidates and deliver increased conversions, hence return you value.