Here's an important topic that we all deal with. All ticketing companies like to "brag" about what they do to help you promote your event.
Most of the major players, like AttendStar, all offer some tools that will assist you in selling more tickets. However, you should never count on those tools to "automatically" sell tickets for you.
Some ticketing companies will send email "blasts" to previous ticket buyers and will often tell you how many names they have on their list. Sending 3,000 emails for an event that has 900 seats "sounds" good, but it's really almost worthless. With open rates around 10% those 3,000 turn into 300. Let's say 5% of the 300 have heard of the artist, so you sell 15 tickets. Not much help.
As email and even texting become overused and abused, the effectiveness of those means are decreasing.
Promotion, in most cases, happens at the local level. Tools that allow buyers and potential buyers to share are some of the best tools you will have. Local radio, posters, flyers still play the most effective promotion for many events.
Look for tools that cause interaction among your target market.