On the one hand, using old icons probably violates the services’ brand use rules but, more importantly, using old icons undermines any attempt to seem web-savvy. I mean, those icons are so 2010-ish!
Here are the brand use guidelines for –
Most of these services have great sets of guidelines for publishers to help them understand how best to use brand assets like logos and buttons. Using old icons is really more a sign of laziness than a lack of adequate resources (which there isn’t). In addition, you’ll often find statements like this which introduce a contractual compliance angle:
By using the Twitter marks, you agree to follow this policy as well as our Terms of Service and all Twitter rules and policies.
So, if you are still using those ancient logos, it’s time to update and be one of the cool kids again.