I am only guessing here, but I think Proximity's client base is very happy with them. They make organizations/events that makes people from various social communities very happy, so they talk and create contents about the client. I mean I guess they do what they do best and make possible for a brand on social networks to exist happily, to be well known.
Proximity Istanbul's expertises are:
Consumer Engagement Strategy & Planning
Social CRM & Social Media
They call themselves "experiential marketing agency specializing in word-of-mouth generating campaigns". That's a very long description, but I must agree with this definition completely. Their events are so good every-time I sacrifice a weekend for them, I ended up very happy and feel worth-whiled. I find myself talking about the event itself to my friends, how fun it was and stuff. If it is not an event, then it is a very personalized gift, which again makes me smile for good amount of time. That is a success for its own-right if nothing-else...
I do not know about the measurable consumer return and other marketing data gathering, but I can easily tell the clients they are working with are happy to engage with consumers in such experimental events over and over again. That alone gives the hint.
Lastly, as far as I can gather from the www they are a part of very big global network actually, over 2000 employees all over the world. I don't know if this information anyhow relevant, but that also gives the hint for it. They are big. They are in lead.