I've known ISFP's and ESFP's that are also not very compassionate. But I think this typically stems from being overly sensitive to their own emotions. It makes it hard for them to be there for others.
My tactic changes from person to person. I think xSFP's are pretty empathetic and can easily adjust or adapt to the person they are trying to connect to and comfort. For some, I'll try and make them laugh. Other times, I just try to hold the person and lend a good ear. Sometimes, it's inviting a person over for some wine and backporch chit chatting, one on one. (This is great for girl talk and ranting.) But I've gotten many people to open up about their problems this way. (Of course, this might be a little weird with strangers.) I just try to assure people that I'm nonjudgmental, and that I'm a trustworthy and compassionate person, that way they'll feel free to open up about whatever is on their mind.