  Searches for persistent gravitational radiation from nonpulsating neutron
stars in young supernova remnants (SNRs) are computationally challenging
because of rapid stellar braking. We describe a practical, efficient,
semi-coherent search based on a hidden Markov model (HMM) tracking scheme,
solved by the Viterbi algorithm, combined with a maximum likelihood matched
filter, the $\mathcal{F}$-statistic. The scheme is well suited to analyzing
data from advanced detectors like the Advanced Laser Interferometer
Gravitational Wave Observatory (Advanced LIGO). It can track rapid phase
evolution from secular stellar braking and stochastic timing noise torques
simultaneously without searching second- and higher-order derivatives of the
signal frequency, providing an economical alternative to stack-slide-based
semi-coherent algorithms. One implementation tracks the signal frequency alone.
A second implementation tracks the signal frequency and its first time
derivative. It improves the sensitivity by a factor of a few upon the first
implementation, but the cost increases by two to three orders of magnitude.
