There are many ways that can be used to make your newly app viral in online market.
1. You can take a help of Facebook ads is it easy and most popular way to get many downloads. even you can use google ads or other ads network help so that you can make your app reach to high number of users.
2. Run a contest.
if you want targeted user for your marketing For example, you can encourage facebook users or other social network user to tweet about your application and get reward by doing this. you can create contest to download app and get paid and many more.
3. Use social networks group.
here is another trick that can be used if you want to promote your android application free. You can can create facebook fans group or fanpage and other groups on social networks. and there you can promote your app which can help you to get many user.
else if you dont have time to take a look all this activity then here you have last option hire some one to do all this task for here is perfect sample where you can buy app reviews and ratings and many more visit here buy app ratings they can create app viral in App-store at really affordable price.