I think it also depends where your start up is on their journey. As @michael.ridgway suggested, being active in social is really important. My last role was at a very early stage tech development company that had no digital presence; developers want to know the thing they’re joining is real so we needed to establish this first.
We handled all our recruiting in house and found each time we advertised, we needed to go to different channels, using both LinkedIn and Seek to promote the roles. This was probably the most important part of our process - writing an advert that stood out from others and compelled developers to apply.
Once you’ve hired one or two into the dev team, you do need them to be out there promoting you as an organisation they want to work at, through meet ups and the like. I always asked one of them to do the screening of candidates as they speak the same language and understand if someone can really do what they are saying. I also involved our team in the whole process of hiring - reviewing the advert, reviewing candidates and interviewing. In a small tech dev team it’s really important they will be able to work together as a team.
Final advice would be, your superstars may end up being the ones that you create not ones created by somewhere else. Look for people you think have the attributes that will help support your brand and keep going back to the market till you find them. These developers are going to shape your company - make sure they’re the right ones!