Sending DMs are a great tool to really create the connection between you and your growing community. Try and make your first message a non-promotional one. There’s few things more annoying than receiving a clearly automated message with a link to buy an unknown product. I don’t know about you, but I certainly don’t go opening links from untrusted brands.
Crowdfire is the most well-known tool that includes bulk messaging. Chances are if you are on twitter, you have received at least one “welcome” message followed by a “via @crowdfire” note.
When it comes to sending bulk direct messages as a means to grow your twitter base, use it as an engagement tool more than a sales tool. Use the message to offer help or show you are open to outreach. This way, a new follower will see the value in continuing to follow your account. You provide not only relevant content, but are responsive and open to engaging with your community.
Only pursue bulk messaging if it’s a way to really add value to your following. If you send messages asking for engagement, you risk angering your community if you do not respond in a timely manner. Sometimes automating your twitter as a “one-man band” can backfire, because you aren’t able to control what you have created. Don’t grow so fast that you can’t keep up with it. You risk damaging your brand.