Not all inclusive, just some good starting points.
One of the first steps should be a defined Mission and Vision Statement for your worship leader/team. See the section on Mission Statements under Updating the Worship Experience for Your Church for more details.
Networking with other churches.
It is always a great idea to network with sister churches for possible talent. Start early and ask for potential leaders to come lead on a specific weekend even if you are not looking right away. Contact your church leadership office in the region and make sure they know you are looking as well.
Many times denominational sites have a careers page that list openings in their churches. If they don’t have that, ask your regional or denominational contact why not.
And while it may seem selfish, you need to keep in mind that a sister church who has an awesome intern on their worship team might not be so willing to play red rover red rover come on over… if they see a need in their own church or opportunities to grow their team to new heights. That should not stop you from asking however.
Church Job boards.
Church job boards like churchjobs.com and churchstaffing.com can be a good source of candidates. There is usually a cost with these posts so use caution. They may even help you write the posting (recommended) to make it easier for you.
Craigslist.
In many cities it is free to post jobs. Some are not but the cost is minimal. The question with Craigslist is how to post the job and under what category. I would recommend posting in two places, under "Jobs" in the "Arts / Media / Design" section to start. You may also want to occasionally post that you are looking in the “Musicians” tab under "connections"….. Many worship leaders I know will troll those ads looking for folks who are looking to play out.
Always make the ad look professional and avoid the temptation to say something like “Position does not pay, but if you want to use your talents for God you found the right place”. That sounds cheesy and sends a message that you don't like to pay for this service. Even if someone is not interested in payment, that can be a turnoff.
Typical ad wording might look something like this...
“Church looking for a Worship Leader or Worship Pastor. We are a (Small, medium, Large) church located in (General area). We run (How many) services on Sunday’s and need someone who can lead by piano or guitar who is familiar with contemporary/modern worship and is comfortable playing hymns as well.
Must be able to grow a team of dedicated servants and foster relationships as this position not only leads the body in worship but builds up those who also serve.
This is a (Part time or full time) position pay is negotiable. Please be prepared to give recommendations and links to YouTube videos of your abilities.”
Ads should mirror your Job Description as much as possible.
Your backyard.
Not your real backyard of course, but the worship team you already have!
Maybe there is someone on the team that has been in the tall grass the whole time just waiting to be called out? How well do you know the team and their abilities? If you as the pastor don’t know everyone that plays on a regular basis on your worship team you have some work to do.
It is very important that you follow the same process for internal candidates that you would for external candidates. Interview them the same way and have them audition for the position.
If there is no one on the team, let them know you are looking and ask them if they know of anyone.
Recruitment is a tough job and must be done 24/7/365.
How old? (Welcome to the litigious era)
Be cautious of telling people you want a “young” worship leader who can relate to the youth in the congregation. This sends the message that worship leaders a little older should not respond and you may be missing out on some very talented people.
There are age discrimination laws that may get you in trouble regardless of your church status. The fact that you are asking people to know contemporary and modern worship songs should be enough.