Stevenage have signed Plymouth defender Scott Laird and Northwood striker Elliott Buchanan, who have both put pen to paper on two-year contracts.
Grimsby striker Isaiah Rankin, 29, has also joined on a free transfer on a deal until the end of the season.
Laird, 19, has been on loan at Broadhall Way for the last month - and Argyle's fee will depend on how his career with Borough progresses.
Buchanan, 18, has scored 23 goals in 26 games for Northwood this season.
Borough boss Peter Taylor had run the rule over the teenager in training.
Grimsby have extended the loan spell of Barnsley defender Rob Atkinson for the rest of the season.