Donald Wood was convicted in his absence of three offences under the Malicious Communications Act 1988 following a trial at Sheffield Crown Court.
The 84-year-old was found guilty by a jury on Friday (25 February) of sending threatening letters to MPs Dan Jarvis, John Healey and Stephanie Peacock between 23 and 27 March 2019.
Wood failed to appear at court for his trial and is believed to have travelled to Morocco.
A warrant for his arrest was issued on 21 February and enquiries are ongoing to trace him.
Wood is due to be sentenced on 5 April 2022. If he has not returned by that date, he will be sentenced in his absence.
Wood is described as white, around 5ft 10ins tall with short, grey, receding hair.
Anyone with information about his whereabouts is asked to call 101 quoting investigation numbers 14/90412/19, 14/53410/19 and 14/52304/19.
Alternatively, you can stay completely anonymous by contacting the independent charity Crimestoppers via their website Crimestoppers-uk.org or by calling their UK Contact Centre on 0800 555 111.