Abel Aguilar agreed to sign for Belenenses through WhatsApp, while Domzale captured Alvaro Brachi via a LinkedIn advert.
Portuguese side Belenenses and Slovenian team Domzale used online services to secure new signings in novel moves during the transfer window.
Belenenses handled negotiations to bring Abel Aguilar to the club from Toulouse, where he was yet to make a Ligue 1 appearance this seasonn, entirely via WhatsApp.
Aguilar featured for Colombia at World Cup 2014 and is seen as a coup for the Lisbon club, with president Rui Pedro Saores revealing all negotiations were handled through the instant messaging application
"The player's agent was in London and the negotiations were all done through WhatsApp messages," Soares said.
"We said what we could offer and they accepted immediately.
"Other clubs with greater financial muscle than us were surprised and asked me how it was possible, because if they knew they would also have tried to sign him."
Domzale also secured a new signing via a social network after coach Luka Elsner posted a message on LinkedIn asking for a "very offensive right-back".
Of the numerous responses, Alvaro Brachi was brought in on a permanent deal following a trial shortly ahead of the deadline.
"NK Domzale only has a small budget, we do not have the money to buy the biggest player," the club's public relations officer Grega Krmavnar said.
"We needed a replacement and could not find one in Slovenia and had no other choice of players. LinkedIn was just an idea from our head coach Luka Elsner, so we decided it would be a good way, so Elsner decided to post it on the site on his profile.
"We watched footage of the best candidates and analysed them. Brachi was the best candidate and we decided to invite him to Slovenia to train with us on a one-week trial and then signed him.
"We needed a player who was out of contract or wanted a change of environment and we think have found a very quality player. I believe we are the first club to find a player in this way."