Searches for resonant and non-resonant pair-produced Higgs bosons () decaying respectively into and (with either a or a boson), with subsequent decays into two leptons and two neutrinos, are presented. The analyses are based on a sample of proton-proton collisions at \sqrt{s} = 13~\mathrm{TeV} at the LHC corresponding to an integrated luminosity of 36~\mathrm{fb}^{-1}. Data and predictions from the standard model are in agreement within uncertainties. For the standard model hypothesis, the data are observed (expected) to exclude a production cross-section times branching ratio of 72~(81^{+42}_{-25})~\mathrm{fb}, corresponding to () times the SM cross section. Lack of deviation from the SM predictions in the observations is used to place constraints on different scenarios considering anomalous couplings which could affect the rate and kinematics of production. In the case of resonant production of a new particle , for mass hypotheses from {\mathrm{m}}_{\mathrm{X}} = 300~\mathrm{GeV} to {\mathrm{m}}_{\mathrm{X}} = 900~\mathrm{GeV}, the data are observed (expected) to exclude a production cross-section times branching ratio of narrow-width spin-0 particles from to ( to )~\mathrm{fb} and narrow-width spin-2 particles from to ( to )~\mathrm{fb}.