It’s a kind gesture with the best of intentions that everyone’s praying for Paris but it’s really the equivalent of doing nothing. If you really want to support them, donate money to the Red Cross, house a stranded French person, or go patronize your favorite French establishment in your city. Those will all go a much longer way than your “prayers,” that’s for sure.
Your local bodega owner, should they be Muslim (and that is also a huge generalization and I’m sorry, but it’s often true and it’s not saying anything negative about them, so step off), is also probably scared shitless right now that they’re going to be attacked because extremists went and did some horrific shit again. Go down and be kind. You can’t blame an entire religion for the actions of a select few, as easy and convenient as it might seem. Every religion, for the most part, has done some horrific shit in the past.
But please, save your prayers because they’re bullshit and they’re not helping anyone but yourself and your piece of mind that you’re “doing your part,” when you’re really not.