Well, one of the most important keys to engaging moving sets is to get them to CHANGE DIRECTION. If they're walking forward and you're just blocking the path, they are still facing their original destination. You haven't fully captured there attention.
This is a good Lance Mason trick: You can ask them for directions, and when you do, you engage a little bit of kino. Walk towards them and point behind them asking something like, "Do you know where Starbucks is? I'm supposed to meet my friends there, but I'm new to this part of town. My friend told me it's in THAT direction, but the directions say it's over THERE." When you say THAT and THERE, you can actually initiate casual kino (hand on the back, or shoulder) and physically turn them by directing their attention into a different direction. When you've got them turned around, you have their full attention and you can proceed with the set as you would any other. Just make sure you keep the attention of the whole group or else one or two of them will start giving each other "wtf...let's get out of here" looks.