Free agent Akinde has agreed a one-month contract - the maximum Pompey are allowed to offer while they remain in administration - after leaving Crawley in January.
Fellow striker Agyemang has arrived on loan from Stevenage and midfielder Racon on the same terms from Millwall.
All three will be in the squad for Saturday's short trip along the south coast to Bournemouth in League One.
Caretaker boss Guy Whittingham could only name four substitutes in the midweek loss at Scunthorpe - Pompey's eighth straight defeat.
