pinterest - i think i can get my name around, some people claim sales from that, but people just want to collect there.
instagram is for phones and bad filters, i honestly wouldn't consider it a social thing.
twitter helps, but you have to target friends well there.
google plus - i was kicked out for advertising, which they said was spamming. i never went back and i apparently am not missing anything.
facebook only works if they seek you out. while i can't say i have sales from there, lately it almost doubled my hits. if someone there likes your work, and they actually credit you with a link, you could get a lot of easy publicity there.
every place you can put your name the better, and with a name like McCoy - as in the The Real McCoy - you can get away with all kinds of advertising
If you are from a smaller city, don't forget to follow your local newspaper on Twitter. I was just asked by my local paper (they just found me on Twitter) if they could do a feature article of me for the weekend paper Bio, picture samples etc YAY.
Facebook - great if you put the time in
Twitter - fabulous if you put the time in
G+ - okay but very busy now. I have had commissions through that
Instagram - not really for sales but you can sell instagram prints on http://instaprints.com our sister site
Pinterest - some people saying they get sales but I have not seen that
As an artist, half of the work is marketing yourself.
Here are some good links to discussions in our forum and elsewhere about marketing your work