To me, there are two things to look at when speaking of recruitment:
1. Getting more people to try out siege - By far the most successful campaign I have seen was the old playsp campaign about 4 years ago, I know that brought a lot of people to Siege. If I remember correctly, there was a website set up, playsp.net or something like that, and there were 4-5 generic sigs all advertising siege and playsp somehow that lots of Siege people used as their main sigs. I would think that it would work wonderfully again, but it would be very hard getting the community that is left to work together to achieve this as well as finding someone dedicated to spearheading this. Just look at the abysmal support Hoffs is getting with the Siege 9 year anniversary, that would have the same effect.
2. Keeping the people who try out siege. From what it seems to me, lots of people try out siege. I would guess we add 10+ new members to NEW a week, and the number of NEW that log in within the past 48 hours is somewhere between 20-30 at any given moment. The problem is keeping them. I would guess that about 50% of the people that join NEW, graduate NEW...and of those graduates, I'm not really sure on this one, but I'd guess another 50% who make it to their next guild eventually die out. So if someone starts on Siege and makes it into NEW, I'd say there's about a 25% chance they actually make Siege their home.
So how do we raise that to 50% or more? Fixing RoT would be good, more shard wide events would be good, more guilds spending time with NEW members, taking them out on hunts and stuff would be good. Those are just my suggestions.